BERKLEY W R CORP, 10-Q filed on 5/1/2026
Quarterly Report
v3.26.1
Cover Page - shares
 3 Months Ended
Mar. 31, 2026
Apr. 27, 2026
Entity Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2026  
Document Transition Report false  
Entity File Number 1-15202  
Entity Registrant Name W. R. BERKLEY CORP  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 22-1867895  
Entity Address, Address Line One 475 Steamboat Road  
Entity Address, City or Town Greenwich  
Entity Address, State or Province CT  
Entity Address, Postal Zip Code 06830  
City Area Code (203)  
Local Phone Number 629-3000  
Title of 12(b) Security Common Stock, par value $.20 per share  
Trading Symbol WRB  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   372,276,732
Entity Central Index Key 0000011544  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Amendment Flag false  
5.700% Subordinated Debentures due 2058    
Entity Information [Line Items]    
Title of 12(b) Security 5.700% Subordinated Debentures due 2058  
Trading Symbol WRB-PE  
Security Exchange Name NYSE  
5.100% Subordinated Debentures due 2059    
Entity Information [Line Items]    
Title of 12(b) Security 5.100% Subordinated Debentures due 2059  
Trading Symbol WRB-PF  
Security Exchange Name NYSE  
4.250% Subordinated Debentures due 2060    
Entity Information [Line Items]    
Title of 12(b) Security 4.250% Subordinated Debentures due 2060  
Trading Symbol WRB-PG  
Security Exchange Name NYSE  
4.125% Subordinated Debentures due 2061    
Entity Information [Line Items]    
Title of 12(b) Security 4.125% Subordinated Debentures due 2061  
Trading Symbol WRB-PH  
Security Exchange Name NYSE  
v3.26.1
Consolidated Balance Sheets Consolidated Balance Sheets - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Investments:    
Fixed maturity securities (amortized cost of $25,814,827 and $25,170,368; allowance for expected credit losses of $306 and $74 at March 31, 2026 and December 31, 2025, respectively) $ 25,508,409 $ 25,047,662
Investment funds 1,398,022 1,361,802
Real estate 1,303,741 1,279,748
Equity securities 1,469,651 1,358,201
Arbitrage trading account 1,164,872 1,221,103
Loans receivable (net of allowance for expected credit losses of $75 and $161 at March 31, 2026 and December 31, 2025, respectively) 441,160 418,913
Total investments 31,285,855 30,687,429
Cash and cash equivalents 2,280,934 2,539,938
Premiums and fees receivable (net of allowance for expected credit losses of $42,130 and $42,006 at March 31, 2026 and December 31, 2025, respectively) 3,470,776 3,417,112
Due from reinsurers (net of allowance for expected credit losses of $4,972 and $6,378 at March 31, 2026 and December 31, 2025, respectively) 3,551,097 3,543,013
Deferred policy acquisition costs 1,012,807 1,000,691
Prepaid reinsurance premiums 870,765 881,831
Trading account receivables from brokers and clearing organizations 8,690 11,669
Property, furniture and equipment 567,116 596,235
Goodwill 184,332 184,332
Accrued investment income 246,022 255,199
Other assets 837,159 809,394
Total assets 44,315,553 43,926,843
Liabilities:    
Reserves for losses and loss expenses 22,616,260 22,207,773
Unearned premiums 6,776,750 6,721,570
Due to reinsurers 627,760 615,781
Trading account securities sold but not yet purchased 33 66,285
Current and deferred federal and foreign income taxes 76,199 39,018
Other liabilities 1,626,900 1,724,797
Subordinated debentures 1,010,707 1,010,527
Senior notes and other debt 1,830,328 1,829,198
Total liabilities $ 34,564,937 34,214,949
Equity:    
Number of authorized shares not disclosed true  
Perferred stock, par value $.10 per share: Authorized 5,000,000 shares; issued and outstanding - none $ 0 0
Common stock, par value $.20 per share: Authorized 500,000,000 shares, issued and outstanding, net of treasury shares, 177,930,502 and 183,411,907 shares, respectively 158,705 158,705
Additional paid-in capital 1,000,375 987,708
Retained earnings 13,825,717 13,344,204
Accumulated other comprehensive loss (601,277) (451,097)
Treasury stock, at cost, 420,822,128 and 416,366,010 shares, respectively (4,643,970) (4,338,702)
Total stockholders’ equity 9,739,550 9,700,818
Noncontrolling interests 11,066 11,076
Total equity 9,750,616 9,711,894
Total liabilities and equity $ 44,315,553 $ 43,926,843
v3.26.1
Consolidated Balance Sheets Consolidated Balance Sheets (Parenthetical) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Statement of Financial Position [Abstract]    
Fixed maturity securities, amortized cost $ 25,814,827 $ 25,170,368
Fixed maturity securities, allowance for credit loss 306 74
Cumulative effect adjustment resulting from changes in accounting principles 75 161
Cumulative effect adjustment resulting from changes in accounting principles 42,130 42,006
Reinsurance recoverable, allowance for credit loss $ 4,972 $ 6,378
Preferred stock, par value (in dollars per share) $ 0.10 $ 0.10
Preferred stock issued (in shares) 5,000,000 5,000,000
Preferred stock outstanding (in shares) 0 0
Common stock, par value (in dollar per share) $ 0.20 $ 0.20
Common shares authorized (in shares)   1,875,000,000
Common shares issued (in shares) 372,699,681 377,155,799
Common shares outstanding (in shares) 372,699,681 377,155,799
Treasury stock issued at cost (in shares) 420,822,128 416,366,010
v3.26.1
Consolidated Statements Income (Unaudited) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
REVENUES:    
Net premiums written $ 3,174,345 $ 3,133,302
Change in net unearned premiums (59,173) (120,921)
Net premiums earned 3,115,172 3,012,381
Net investment income 404,333 360,292
Net realized and unrealized (losses) gains on investments (15,629) 15,711
Change in allowance for expected credit losses on investments (146) 644
Net investment (losses) gains (15,775) 16,355
Revenues from non-insurance businesses 156,551 128,909
Insurance service fees 28,230 28,929
Other income 1,823 533
Total revenues 3,690,334 3,547,399
OPERATING COSTS AND EXPENSES:    
Losses and loss expenses 1,936,025 1,900,792
Other operating costs and expenses 970,660 949,910
Expenses from non-insurance businesses 135,842 126,364
Interest expense 31,709 31,727
Total 3,074,236 3,008,793
Income before income taxes 616,098 538,606
Income tax expense (100,523) (121,257)
Net income before noncontrolling interests 515,575 417,349
Noncontrolling interests (359) 222
Net Income (Loss) to Common Stockholders $ 515,216 $ 417,571
NET INCOME PER SHARE:    
Basic (in dollar per share) $ 1.31 $ 1.05
Diluted (in dollar per share) $ 1.31 $ 1.04
v3.26.1
Consolidated Statements of Comprehensive Income (Unaudited) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Statement of Comprehensive Income [Abstract]    
Net income before noncontrolling interests $ 515,575 $ 417,349
Other comprehensive (loss) income:    
Change in unrealized currency translation adjustments (5,224) 23,930
Change in unrealized investment (losses) gains, net of taxes (144,956) 148,273
Other comprehensive (loss) income (150,180) 172,203
Comprehensive income 365,395 589,552
Noncontrolling interests (359) 223
Comprehensive income to common stockholders $ 365,036 $ 589,775
v3.26.1
Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($)
$ in Thousands
Total
Common stock
Additional paid-in capital
Retained earnings
Unrealized investment losses:
Change in unrealized (losses) gains on securities without an allowance for expected credit losses
Change in unrealized losses on securities with an allowance for expected credit losses
Currency translation adjustments:
Accumulated Other Comprehensive Income (Loss)
Treasury stock
Noncontrolling interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]                      
Cumulative effect adjustment resulting from changes in accounting principles   $ 158,705 $ 984,825 $ 12,265,070 $ (517,170)     $ (417,099) $ (934,269) $ (4,079,220) $ 12,328
Beginning of period at Dec. 31, 2024   158,705 984,825 12,265,070 (517,170)     (417,099) (934,269) (4,079,220) 12,328
Increase (Decrease) in Stockholders' Equity [Roll Forward]                      
Restricted stock units issued     (4,347)                
Restricted stock units expensed     12,423                
Net income before noncontrolling interests $ 417,349     417,571             (222)
Dividends ($0.09 and $0.08 per share, respectively)       (30,338)              
Change in unrealized (losses) gains on securities without an allowance for expected credit losses 148,273         $ 148,823          
Change in unrealized losses on securities with an allowance for expected credit losses             $ (551)        
Net change in period 23,930             23,930      
Stock exercised/vested                   1,050  
Stock repurchased                   (49,202)  
Other (431)                    
(Distributions) contributions                     228
Other comprehensive income (loss), net of tax $ 172,203       148,273     23,930 172,203   (1)
End of period at Mar. 31, 2025     992,901 12,652,303 (368,898)     (393,169) (762,067) (4,127,803) 12,333
Increase (Decrease) in Stockholders' Equity [Roll Forward]                      
Common stock dividends, per share, cash paid (in dollars per share) $ 0.08                    
Cumulative effect adjustment resulting from changes in accounting principles     992,901 12,652,303 (368,898)     (393,169) (762,067) (4,127,803) 12,333
Cumulative effect adjustment resulting from changes in accounting principles $ 9,711,894 158,705 987,708 13,344,205 (124,680)     (326,417) (451,097) (4,338,702) 11,076
Beginning of period at Dec. 31, 2025 9,711,894 $ 158,705 987,708 13,344,205 (124,680)     (326,417) (451,097) (4,338,702) 11,076
Increase (Decrease) in Stockholders' Equity [Roll Forward]                      
Restricted stock units issued     (567)                
Restricted stock units expensed     13,234                
Net income before noncontrolling interests 515,575     515,216             359
Dividends ($0.09 and $0.08 per share, respectively)       (33,704)              
Change in unrealized (losses) gains on securities without an allowance for expected credit losses (144,956)         $ (144,954)          
Change in unrealized losses on securities with an allowance for expected credit losses             $ (2)        
Net change in period (5,224)             (5,224)      
Stock exercised/vested                   178  
Stock repurchased                   (302,432)  
Other (3,014)                    
(Distributions) contributions                     (369)
Other comprehensive income (loss), net of tax (150,180)       (144,956)     (5,224) (150,180)   0
End of period at Mar. 31, 2026 $ 9,750,616   1,000,375 13,825,717 (269,636)     (331,641) (601,277) (4,643,970) 11,066
Increase (Decrease) in Stockholders' Equity [Roll Forward]                      
Common stock dividends, per share, cash paid (in dollars per share) $ 0.09                    
Cumulative effect adjustment resulting from changes in accounting principles $ 9,750,616   $ 1,000,375 $ 13,825,717 $ (269,636)     $ (331,641) $ (601,277) $ (4,643,970) $ 11,066
v3.26.1
Consolidated Statements of Cash Flows (Unaudited) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
CASH FROM OPERATING ACTIVITIES:    
Net income to common stockholders $ 515,216 $ 417,571
Adjustments to reconcile net income to net cash from operating activities:    
Net investment losses (gains) 15,775 (16,355)
Depreciation and (accretion) amortization (15,466) (9,786)
Noncontrolling interests 359 (222)
Investment funds (39,529) (27,023)
Stock incentive plans 13,234 12,423
Change in:    
Arbitrage trading account (7,041) (13,525)
Premiums and fees receivable (48,652) (43,844)
Reinsurance accounts 15,249 (42,956)
Deferred policy acquisition costs (10,377) (26,822)
Income taxes 77,266 134,962
Reserves for losses and loss expenses 390,620 544,204
Unearned premiums 47,872 113,060
Other (286,669) (297,870)
Net cash from operating activities 667,857 743,817
CASH USED IN INVESTING ACTIVITIES:    
Proceeds from sale of fixed maturity securities 271,595 290,625
Proceeds from sale of equity securities 4,573 132,663
(Contributions to) distributions from investment funds (4,030) 16,295
Proceeds from maturities and prepayments of fixed maturity securities 1,360,093 1,198,698
Purchase of fixed maturity securities (2,217,950) (2,486,160)
Purchase of equity securities (120,517) (56,564)
Real estate purchased (37,431) (14,785)
Change in loans receivable (30,581) (3,694)
Net proceeds from sale (purchases) of property, furniture and equipment 27,670 (16,201)
Change in balances due to security brokers 157,986 14,705
Net cash used in investing activities (588,592) (924,418)
CASH USED IN FINANCING ACTIVITIES:    
Net proceeds from issuance of debt 1,105 1,638
Cash dividends to common stockholders (33,704) (30,338)
Purchase of common treasury shares (302,432) (49,202)
Other, net (4,079) (3,508)
Net cash used in financing activities (339,110) (81,410)
Net impact on cash due to change in foreign exchange rates 841 7,473
Net change in cash and cash equivalents (259,004) (254,538)
Cash and cash equivalents at beginning of period 2,539,938 1,974,747
Cash and cash equivalents at end of period $ 2,280,934 $ 1,720,209
v3.26.1
Statement of Cash Flows
 3 Months Ended
Mar. 31, 2026
Supplemental Cash Flow Elements [Abstract]  
Statements of Cash Flows Statements of Cash Flows    Interest payments were $41,245,000 and $41,193,000 for the three months ended March 31, 2026 and 2025, respectively. Income tax refunds were $614,000 and $18,740,000 for the three months ended March 31, 2026 and 2025, respectively.
v3.26.1
General
 3 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]  
General General
    The unaudited consolidated financial statements, which include the accounts of W. R. Berkley Corporation and its subsidiaries (the “Company”), have been prepared on the basis of U.S. generally accepted accounting principles (“GAAP”) for interim financial information. Accordingly, they do not include all the information and notes required by GAAP for annual financial statements. The unaudited consolidated financial statements reflect all adjustments, consisting only of normal recurring items, which are necessary to present fairly the Company’s financial position and results of operations on a basis consistent with the prior audited consolidated financial statements. Operating results for interim periods are not necessarily indicative of the results that may be expected for the year. All significant intercompany accounts and transactions have been eliminated.
The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the revenues and expenses reflected during the reporting period. For further information related to areas of judgment and estimates and other information necessary to understand the Company’s financial position and results of operations, refer to the audited consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025.
For interim periods, the income tax provision is based upon the Company’s estimated annual effective tax rate. This rate is greater than the federal income tax rate of 21%, primarily due to the geographical mix of earnings and amounts being subject to tax at a rate greater than the U.S. statutory rate and state taxes, which are partially offset by tax benefits related to tax-exempt investment income. Tax benefits related to equity-based compensation or other non-recurring items are discretely recorded in the period in which it occurs.
v3.26.1
Per Share Data
 3 Months Ended
Mar. 31, 2026
Earnings Per Share [Abstract]  
Per Share Data Per Share Data
    The Company presents both basic and diluted net income per share (“EPS”) amounts. Basic EPS is calculated by dividing net income by the weighted average number of common shares outstanding during the period (including 17,378,810 and 17,659,297 common shares held in a grantor trust as of March 31, 2026 and 2025, respectively). The common shares held in the grantor trust are designated for delivery upon the settlement of restricted stock units ("RSUs") that are vested but mandatorily deferred. Accordingly, such shares deliverable under vested RSUs do not affect diluted shares outstanding since the shares are already included in basic shares outstanding (which includes the shares in the grantor trust referenced above). Diluted EPS is based upon the weighted average number of basic and common equivalent shares outstanding during the period and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect.
    The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows:
For the Three Months
Ended March 31,
(In thousands)20262025
Basic392,264 396,929 
Diluted394,779 399,825 
v3.26.1
Recent Accounting Pronouncements and Accounting Policies
 3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
Recent Accounting Pronouncements and Accounting Policies Recent Accounting Pronouncements and Accounting Policies
Recently adopted accounting pronouncements:
    All accounting and reporting standards that became effective in 2026 were either not applicable to the Company or their adoption did not have a material impact on the Company.
Accounting and reporting standards that are not yet effective:

    In November 2024, the Financial Accounting Standards Board issued Accounting Standards Update 2024-03, Disaggregation of Income Statement Expenses, addressing investor requests for more transparent information. The guidance requires disclosure of specified information about certain costs and expenses in the notes to the financial statements. The guidance is effective for annual periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. Prospective application is required, with retrospective application permitted. The Company will adopt this guidance for the year ended December 31, 2027 and the resulting impact will be disclosure only.
All other recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.
v3.26.1
Consolidated Statements of Comprehensive Income (Loss)
 3 Months Ended
Mar. 31, 2026
Equity [Abstract]  
Consolidated Statements of Comprehensive Income (Loss) Consolidated Statements of Comprehensive Income
    The following tables present the components of the changes in accumulated other comprehensive (loss) income ("AOCI"):

(In thousands)Unrealized Investment (Losses) Gains Currency Translation AdjustmentsAccumulated Other Comprehensive (Loss) Income
As of and for the three months ended March 31, 2026
Changes in AOCI
Beginning of period$(124,680)$(326,417)$(451,097)
Other comprehensive loss before reclassifications(148,410)(5,224)(153,634)
Amounts reclassified from AOCI3,454 — 3,454 
Other comprehensive loss(144,956)(5,224)(150,180)
Unrealized investment loss related to noncontrolling interest— — — 
End of period$(269,636)$(331,641)$(601,277)
Amounts reclassified from AOCI
Pre-tax$4,372 (1)$— $4,372 
Tax effect (918)(2)— (918)
After-tax amounts reclassified$3,454 $— $3,454 
Other comprehensive loss
Pre-tax$(185,971)$(5,224)$(191,195)
Tax effect41,015 — 41,015 
Other comprehensive loss$(144,956)$(5,224)$(150,180)

As of and for the three months ended March 31, 2025
Changes in AOCI
Beginning of period$(517,170)$(417,099)$(934,269)
Other comprehensive income before reclassifications144,102 23,930 168,032 
Amounts reclassified from AOCI4,171 — 4,171 
Other comprehensive income148,273 23,930 172,203 
Unrealized investment loss related to noncontrolling interest(1)— (1)
End of period$(368,898)$(393,169)$(762,067)
Amounts reclassified from AOCI
Pre-tax$5,280 (1)$— $5,280 
Tax effect (1,109)(2)— (1,109)
After-tax amounts reclassified$4,171 $— $4,171 
Other comprehensive income
Pre-tax$185,855 $23,930 $209,785 
Tax effect(37,582)— (37,582)
Other comprehensive income$148,273 $23,930 $172,203 
____________
(1) Net investment (losses) gains in the consolidated statements of income.
(2) Income tax expense in the consolidated statements of income.
v3.26.1
Investments In Fixed Maturity Securities
 3 Months Ended
Mar. 31, 2026
Investments, Debt and Equity Securities [Abstract]  
Investments In Fixed Maturity Securities Investments in Fixed Maturity Securities
    At March 31, 2026 and December 31, 2025, investments in fixed maturity securities were as follows:
 
(In thousands)Amortized
Cost		Allowance for Expected Credit Losses (1)Gross UnrealizedFair
Value		Carrying
Value
GainsLosses
March 31, 2026
Held to maturity:
State and municipal$29,182 $— $552 $— $29,734 $29,182 
Residential mortgage-backed1,743 — 57 — 1,800 1,743 
Total held to maturity30,925 — 609 — 31,534 30,925 
Available for sale:
U.S. government and government agency4,378,606 — 37,479 (32,512)4,383,573 4,383,573 
State and municipal:
Special revenue1,130,177 — 5,252 (27,159)1,108,270 1,108,270 
State general obligation201,814 — 2,287 (3,804)200,297 200,297 
Pre-refunded73,923 — 721 (32)74,612 74,612 
Corporate backed159,306 — 1,261 (3,374)157,193 157,193 
Local general obligation213,685 — 969 (3,219)211,435 211,435 
Total state and municipal1,778,905 — 10,490 (37,588)1,751,807 1,751,807 
Mortgage-backed:
Residential4,592,286 (77)44,169 (138,303)4,498,075 4,498,075 
Commercial218,847 — 3,172 (36)221,983 221,983 
Total mortgage-backed4,811,133 (77)47,341 (138,339)4,720,058 4,720,058 
Asset-backed3,881,752 (229)10,025 (22,603)3,868,945 3,868,945 
Corporate:
Industrial3,514,642 — 36,565 (39,478)3,511,729 3,511,729 
Financial3,526,804 — 34,606 (26,851)3,534,559 3,534,559 
Utilities1,521,021 — 12,721 (14,083)1,519,659 1,519,659 
Other209,346 — 1,365 (488)210,223 210,223 
Total corporate8,771,813 — 85,257 (80,900)8,776,170 8,776,170 
Foreign government2,161,693 — 16,184 (200,946)1,976,931 1,976,931 
Total available for sale25,783,902 (306)206,776 (512,888)25,477,484 25,477,484 
Total investments in fixed maturity securities$25,814,827 $(306)$207,385 $(512,888)$25,509,018 $25,508,409 
____________
(1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors.
(In thousands)Amortized
Cost		Allowance for Expected Credit Losses (1)Gross UnrealizedFair
Value		Carrying
Value
GainsLosses
December 31, 2025
Held to maturity:
State and municipal$28,777 $(9)$796 $— $29,564 $28,768 
Residential mortgage-backed1,838 — 76 — 1,914 1,838 
Total held to maturity30,615 (9)872 — 31,478 30,606 
Available for sale:
U.S. government and government agency3,964,375 — 48,820 (15,157)3,998,038 3,998,038 
State and municipal:
Special revenue1,206,387 — 6,002 (27,943)1,184,446 1,184,446 
State general obligation203,543 — 3,465 (3,848)203,160 203,160 
Pre-refunded74,276 — 619 (111)74,784 74,784 
Corporate backed159,876 — 1,958 (3,459)158,375 158,375 
Local general obligation218,022 — 1,459 (3,052)216,429 216,429 
Total state and municipal1,862,104 — 13,503 (38,413)1,837,194 1,837,194 
Mortgage-backed:
Residential4,584,970 (65)71,048 (132,645)4,523,308 4,523,308 
Commercial281,573 — 3,632 (35)285,170 285,170 
Total mortgage-backed4,866,543 (65)74,680 (132,680)4,808,478 4,808,478 
Asset-backed3,807,393 — 20,196 (17,243)3,810,346 3,810,346 
Corporate:
Industrial3,627,567 — 57,466 (36,499)3,648,534 3,648,534 
Financial3,438,348 — 61,180 (16,460)3,483,068 3,483,068 
Utilities1,300,506 — 22,593 (8,878)1,314,221 1,314,221 
Other240,374 — 2,356 (1,142)241,588 241,588 
Total corporate8,606,795 — 143,595 (62,979)8,687,411 8,687,411 
Foreign government2,032,543 — 20,906 (177,860)1,875,589 1,875,589 
Total available for sale25,139,753 (65)321,700 (444,332)25,017,056 25,017,056 
Total investments in fixed maturity securities$25,170,368 $(74)$322,572 $(444,332)$25,048,534 $25,047,662 
____________
(1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors.
The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2026 and 2025:
(In thousands)20262025
Balance, beginning of period$9 $25 
Provision for expected credit losses(9)(5)
Balance, end of period$— $20 
The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2026 and 2025:
20262025
(In thousands)Foreign GovernmentMortgage-backedAsset-backedState and MunicipalTotalForeign GovernmentMortgage-backedAsset-backedState and MunicipalTotal
Balance, beginning of period$— $65 $— $— $65 $216 $430 $— $— $646 
Change on securities for which credit losses were not previously recorded— — 229 — 229 — — — 10 10 
Change on securities for which credit losses were previously recorded— 12 — — 12 107 (430)— — (323)
Balance, end of period$— $77 $229 $— $306 $323 $— $— $10 $333 
During the three months ended March 31, 2026, the Company increased the allowance for expected credit losses for available for sale securities primarily due to a decrease in the fair value of one investment in the asset-backed category. During the three months ended March 31, 2025, the Company decreased the allowance for expected credit losses for available for sale securities primarily due to improved pricing related to mortgage-backed securities.
The amortized cost and fair value of fixed maturity securities at March 31, 2026, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations.  
(In thousands)Amortized
Cost 		Fair
Value
Due in one year or less$1,859,542 $1,811,447 
Due after one year through five years7,947,108 7,814,089 
Due after five years through ten years3,963,797 3,959,533 
Due after ten years7,231,504 7,202,091 
Mortgage-backed securities4,812,876 4,721,858 
Total$25,814,827 $25,509,018 
________________    
At March 31, 2026 and December 31, 2025, there were no investments that exceeded 10% of common stockholders' equity, other than investments in United States government and government agency securities.
v3.26.1
Investments in Equity Securities
 3 Months Ended
Mar. 31, 2026
Debt Securities, Available-for-sale [Line Items]  
Investments in Equity Securities Investments in Fixed Maturity Securities
    At March 31, 2026 and December 31, 2025, investments in fixed maturity securities were as follows:
 
(In thousands)Amortized
Cost		Allowance for Expected Credit Losses (1)Gross UnrealizedFair
Value		Carrying
Value
GainsLosses
March 31, 2026
Held to maturity:
State and municipal$29,182 $— $552 $— $29,734 $29,182 
Residential mortgage-backed1,743 — 57 — 1,800 1,743 
Total held to maturity30,925 — 609 — 31,534 30,925 
Available for sale:
U.S. government and government agency4,378,606 — 37,479 (32,512)4,383,573 4,383,573 
State and municipal:
Special revenue1,130,177 — 5,252 (27,159)1,108,270 1,108,270 
State general obligation201,814 — 2,287 (3,804)200,297 200,297 
Pre-refunded73,923 — 721 (32)74,612 74,612 
Corporate backed159,306 — 1,261 (3,374)157,193 157,193 
Local general obligation213,685 — 969 (3,219)211,435 211,435 
Total state and municipal1,778,905 — 10,490 (37,588)1,751,807 1,751,807 
Mortgage-backed:
Residential4,592,286 (77)44,169 (138,303)4,498,075 4,498,075 
Commercial218,847 — 3,172 (36)221,983 221,983 
Total mortgage-backed4,811,133 (77)47,341 (138,339)4,720,058 4,720,058 
Asset-backed3,881,752 (229)10,025 (22,603)3,868,945 3,868,945 
Corporate:
Industrial3,514,642 — 36,565 (39,478)3,511,729 3,511,729 
Financial3,526,804 — 34,606 (26,851)3,534,559 3,534,559 
Utilities1,521,021 — 12,721 (14,083)1,519,659 1,519,659 
Other209,346 — 1,365 (488)210,223 210,223 
Total corporate8,771,813 — 85,257 (80,900)8,776,170 8,776,170 
Foreign government2,161,693 — 16,184 (200,946)1,976,931 1,976,931 
Total available for sale25,783,902 (306)206,776 (512,888)25,477,484 25,477,484 
Total investments in fixed maturity securities$25,814,827 $(306)$207,385 $(512,888)$25,509,018 $25,508,409 
____________
(1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors.
(In thousands)Amortized
Cost		Allowance for Expected Credit Losses (1)Gross UnrealizedFair
Value		Carrying
Value
GainsLosses
December 31, 2025
Held to maturity:
State and municipal$28,777 $(9)$796 $— $29,564 $28,768 
Residential mortgage-backed1,838 — 76 — 1,914 1,838 
Total held to maturity30,615 (9)872 — 31,478 30,606 
Available for sale:
U.S. government and government agency3,964,375 — 48,820 (15,157)3,998,038 3,998,038 
State and municipal:
Special revenue1,206,387 — 6,002 (27,943)1,184,446 1,184,446 
State general obligation203,543 — 3,465 (3,848)203,160 203,160 
Pre-refunded74,276 — 619 (111)74,784 74,784 
Corporate backed159,876 — 1,958 (3,459)158,375 158,375 
Local general obligation218,022 — 1,459 (3,052)216,429 216,429 
Total state and municipal1,862,104 — 13,503 (38,413)1,837,194 1,837,194 
Mortgage-backed:
Residential4,584,970 (65)71,048 (132,645)4,523,308 4,523,308 
Commercial281,573 — 3,632 (35)285,170 285,170 
Total mortgage-backed4,866,543 (65)74,680 (132,680)4,808,478 4,808,478 
Asset-backed3,807,393 — 20,196 (17,243)3,810,346 3,810,346 
Corporate:
Industrial3,627,567 — 57,466 (36,499)3,648,534 3,648,534 
Financial3,438,348 — 61,180 (16,460)3,483,068 3,483,068 
Utilities1,300,506 — 22,593 (8,878)1,314,221 1,314,221 
Other240,374 — 2,356 (1,142)241,588 241,588 
Total corporate8,606,795 — 143,595 (62,979)8,687,411 8,687,411 
Foreign government2,032,543 — 20,906 (177,860)1,875,589 1,875,589 
Total available for sale25,139,753 (65)321,700 (444,332)25,017,056 25,017,056 
Total investments in fixed maturity securities$25,170,368 $(74)$322,572 $(444,332)$25,048,534 $25,047,662 
____________
(1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors.
The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2026 and 2025:
(In thousands)20262025
Balance, beginning of period$9 $25 
Provision for expected credit losses(9)(5)
Balance, end of period$— $20 
The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2026 and 2025:
20262025
(In thousands)Foreign GovernmentMortgage-backedAsset-backedState and MunicipalTotalForeign GovernmentMortgage-backedAsset-backedState and MunicipalTotal
Balance, beginning of period$— $65 $— $— $65 $216 $430 $— $— $646 
Change on securities for which credit losses were not previously recorded— — 229 — 229 — — — 10 10 
Change on securities for which credit losses were previously recorded— 12 — — 12 107 (430)— — (323)
Balance, end of period$— $77 $229 $— $306 $323 $— $— $10 $333 
During the three months ended March 31, 2026, the Company increased the allowance for expected credit losses for available for sale securities primarily due to a decrease in the fair value of one investment in the asset-backed category. During the three months ended March 31, 2025, the Company decreased the allowance for expected credit losses for available for sale securities primarily due to improved pricing related to mortgage-backed securities.
The amortized cost and fair value of fixed maturity securities at March 31, 2026, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations.  
(In thousands)Amortized
Cost 		Fair
Value
Due in one year or less$1,859,542 $1,811,447 
Due after one year through five years7,947,108 7,814,089 
Due after five years through ten years3,963,797 3,959,533 
Due after ten years7,231,504 7,202,091 
Mortgage-backed securities4,812,876 4,721,858 
Total$25,814,827 $25,509,018 
________________    
At March 31, 2026 and December 31, 2025, there were no investments that exceeded 10% of common stockholders' equity, other than investments in United States government and government agency securities.
Equity Securities  
Debt Securities, Available-for-sale [Line Items]  
Investments in Equity Securities Investments in Equity Securities
    At March 31, 2026 and December 31, 2025, investments in equity securities were as follows:
 
(In thousands)CostGross UnrealizedFair
Value		Carrying
Value
GainsLosses
March 31, 2026
Common stocks$602,744 $255,501 $(8,575)$849,670 $849,670 
Preferred stocks513,249 112,647 (5,915)619,981 619,981 
Total$1,115,993 $368,148 $(14,490)$1,469,651 $1,469,651 
December 31, 2025
Common stocks$566,577 $181,120 $(5,584)$742,113 $742,113 
Preferred stocks433,472 187,891 (5,275)616,088 616,088 
Total$1,000,049 $369,011 $(10,859)$1,358,201 $1,358,201 
v3.26.1
Arbitrage Trading Account
 3 Months Ended
Mar. 31, 2026
Debt Securities, Trading, and Equity Securities, FV-NI [Abstract]  
Arbitrage Trading Account Arbitrage Trading Account
    At March 31, 2026 and December 31, 2025, the fair and carrying values of the arbitrage trading account were $1,165 million and $1,221 million, respectively. The primary focus of the trading account is merger arbitrage. Merger arbitrage is the business of investing in the securities of publicly held companies which are the targets in announced tender offers and mergers. Arbitrage investing differs from other types of investing in its focus on transactions and events believed likely to bring about a change in value over a relatively short time period (usually four months or less).
    The Company uses put options and call options in order to mitigate the impact of potential changes in market conditions on the merger arbitrage trading account. These options are reported at fair value. As of March 31, 2026, the fair value of short option contracts was $33 thousand (notional amount of $1 million). Other than with respect to the use of these trading account securities, the Company does not make use of derivatives.
v3.26.1
Net Investment Income
 3 Months Ended
Mar. 31, 2026
Net Investment Income [Abstract]  
Net Investment Income Net Investment Income
    Net investment income consisted of the following: 
 For the Three Months
Ended March 31,
(In thousands)20262025
Investment income (loss) earned on:
Fixed maturity securities, including cash and cash equivalents and loans receivable$346,527 $313,788 
Investment funds39,529 27,023 
Equity securities15,819 10,641 
Arbitrage trading account (1)10,313 16,329 
Real estate(4,933)(4,017)
Gross investment income407,255 363,764 
Investment expense(2,922)(3,472)
Net investment income$404,333 $360,292 
(1) Net investment income includes earnings from trading account receivables from brokers and clearing organizations.
v3.26.1
Investment Funds
 3 Months Ended
Mar. 31, 2026
Equity Method Investments and Joint Ventures [Abstract]  
Investment Funds Investment Funds
    The Company evaluates whether it is an investor in a variable interest entity ("VIE"). Such entities do not have sufficient equity at risk to finance their activities without additional subordinated financial support, or the equity investors, as a group, do not have the characteristics of a controlling financial interest (primary beneficiary). The Company determines whether it is the primary beneficiary of an entity subject to consolidation based on a qualitative assessment of the VIE's capital structure, contractual terms, nature of the VIE's operations and purpose, and the Company's relative exposure to the related risks of the VIE on the date it becomes initially involved in the VIE and on an ongoing basis. The Company is not the primary beneficiary in any of its investment funds, and accordingly, carries its interests in investment funds under the equity method of accounting.    
    The Company’s maximum exposure to loss with respect to these investments is limited to the carrying amount reported on the Company’s consolidated balance sheet and its unfunded commitments, which were $251 million as of March 31, 2026.
    Investment funds consisted of the following:
Carrying Value as of Income (Loss) from
Investment Funds
March 31,December 31,For the Three Months
Ended March 31,
(In thousands)2026202520262025
Financial services (1)$365,731 $360,320 $7,402 $7,114 
Transportation275,546 272,775 8,660 8,615 
Real Estate157,089 163,098 8,016 4,965 
Infrastructure176,316 169,847 5,792 3,502 
Energy43,565 41,966 2,433 (2,102)
Other funds379,775 353,796 7,226 4,929 
Total$1,398,022 $1,361,802 $39,529 $27,023 
(1) Includes the Company's minority investment in Lifson Re (see Note 23 Related-Party Transactions).
    The Company's share of the earnings or losses from investment funds is generally reported on a one-quarter lag in order to facilitate the timely completion of the Company's consolidated financial statements.
Other funds include deferred compensation trust assets of $47 million and $43 million as of March 31, 2026 and December 31, 2025, respectively. These assets support other liabilities reflected in the balance sheet of an equal amount for employees who have elected to defer a portion of their compensation. The change in the net asset value of the trust is recorded in other funds within net investment income with an offsetting equal amount within corporate expenses.
v3.26.1
Real Estate
 3 Months Ended
Mar. 31, 2026
Real Estate [Abstract]  
Real Estate Real Estate
    Investment in real estate represents directly owned property held for investment, as follows:
Carrying Value
March 31,December 31,
(In thousands)20262025
Properties in operation$1,075,345 $1,051,455 
Properties under development228,396 228,293 
Total$1,303,741 $1,279,748 

    As of March 31, 2026, properties in operation included a long-term ground lease in Washington, D.C., an office complex in New York City and the completed portion of a mixed-use project in Washington, D.C. Properties in operation are net of accumulated depreciation and amortization of $44,088,000 and $41,942,000 as of March 31, 2026 and December 31, 2025, respectively. Related depreciation expense was $2,570,000 and $2,228,000 for the three months ended March 31, 2026 and 2025, respectively. Future minimum rental income expected on operating leases relating to properties in operation is $28,469,051 in 2026, $41,187,585 in 2027, $44,955,741 in 2028, $40,347,609 in 2029, $34,499,456 in 2030, $29,851,700 in 2031 and $362,556,463 thereafter.
    A mixed-use project in Washington, D.C. had been under development in 2026 and 2025. The completed portion of the project is reported in properties in operation.
v3.26.1
Loans Receivable
 3 Months Ended
Mar. 31, 2026
Receivables [Abstract]  
Loans Receivable Loans Receivable
At March 31, 2026 and December 31, 2025, loans receivable were as follows:
(In thousands)March 31,
2026		December 31,
2025
Amortized cost (net of allowance for expected credit losses):
Real estate loans$441,160 $418,913 
Fair value:
Real estate loans$441,236 $419,074 
The real estate loans are secured by commercial and residential real estate primarily located in the U.K. and New York. These loans generally earn interest at fixed or variable interest rates and have maturities through 2030.
The following table presents the rollforward of the allowance for expected credit losses for loans receivable for the three months ended March 31, 2026 and 2025:
20262025
(In thousands)Real Estate LoansCommercial LoansTotalReal Estate LoansCommercial LoansTotal
Balance, beginning of period$161 $— $161 $1,088 $26 $1,114 
Change in expected credit losses(86)— (86)(312)(14)(326)
Balance, end of period$75 $— $75 $776 $12 $788 
During the three months ended March 31, 2026 and 2025, the Company decreased the allowance for expected credit losses due to a decrease in the weighted average life of the remaining loan portfolio.
The Company monitors the performance of its loans receivable and assesses the ability of the borrower to pay principal and interest based upon loan structure, underlying property values, cash flow and related financial and operating performance of the property and market conditions.
    In evaluating the real estate loans, the Company considers their credit quality indicators, including loan to value ratios, which compare the outstanding loan amount to the estimated value of the property, the borrower’s financial condition and performance with respect to loan terms, the position in the capital structure, the overall leverage in the capital structure and other market conditions.
v3.26.1
Net Investment (Losses) Gains
 3 Months Ended
Mar. 31, 2026
Realized and Unrealized Investment Gains (Losses) [Abstract]  
Net Investment (Losses) Gains Net Investment (Losses) Gains
     Net investment (losses) gains were as follows:
For the Three Months
Ended March 31,
(In thousands)20262025
Net investment (losses) gains:
Fixed maturity securities:
Gains$5,148 $2,632 
Losses(6,537)(2,712)
Equity securities (1):
Net realized gains (losses) on investment sales 1 (2,595)
Change in unrealized (losses) gains (4,494)19,947 
Investment funds173 14 
Real estate (7,298)3,943 
Loans receivable131 — 
Other(2,753)(5,518)
Net realized and unrealized (losses) gains on investments in earnings before allowance for expected credit losses(15,629)15,711 
Change in allowance for expected credit losses on investments:
Fixed maturity securities(232)318 
Loans receivable86 326 
Change in allowance for expected credit losses on investments(146)644 
Net investment (losses) gains(15,775)16,355 
Income tax benefit (expense)3,381 (3,528)
After-tax net investment (losses) gains$(12,394)$12,827 
Change in unrealized investment (losses) gains on available for sale securities:
Fixed maturity securities without allowance for expected credit losses$(183,478)$183,987 
Fixed maturity securities with allowance for expected credit losses(2)(551)
Investment funds(2,519)2,496 
Other28 (77)
Total change in unrealized investment (losses) gains(185,971)185,855 
Income tax benefit (expense)41,015 (37,582)
Noncontrolling interests— (1)
After-tax change in unrealized investment (losses) gains of available for sale securities$(144,956)$148,272 
______________________
(1) The net realized gains or losses on investment sales represent the total gains or losses from the purchase dates of the equity securities. The change in unrealized gains (losses) consists of two components: (i) the reversal of the gain or loss recognized in previous periods on equity securities sold and (ii) the change in unrealized gain or loss resulting from mark-to-market adjustments on equity securities still held.
v3.26.1
Fixed Maturity Securities In An Unrealized Loss Position
 3 Months Ended
Mar. 31, 2026
Investments, Debt and Equity Securities [Abstract]  
Fixed Maturity Securities In An Unrealized Loss Position Fixed Maturity Securities in an Unrealized Loss Position
    The following tables summarize all fixed maturity securities in an unrealized loss position at March 31, 2026 and December 31, 2025 by the length of time those securities have been continuously in an unrealized loss position:
  Less Than 12 Months12 Months or GreaterTotal
(In thousands)Fair
Value		Gross
Unrealized Losses		Fair
Value		Gross
Unrealized Losses		Fair
Value		Gross
Unrealized Losses
March 31, 2026
U.S. government and government agency$1,605,859 $27,355 $134,391 $5,157 $1,740,250 $32,512 
State and municipal272,890 2,390 919,184 35,198 1,192,074 37,588 
Mortgage-backed960,232 11,297 683,839 127,042 1,644,071 138,339 
Asset-backed1,565,320 6,184 518,177 16,419 2,083,497 22,603 
Corporate1,963,231 24,464 1,538,307 56,436 3,501,538 80,900 
Foreign government1,052,525 20,046 252,591 180,900 1,305,116 200,946 
Fixed maturity securities$7,420,057 $91,736 $4,046,489 $421,152 $11,466,546 $512,888 
December 31, 2025
U.S. government and government agency$790,077 $8,902 $183,896 $6,255 $973,973 $15,157 
State and municipal141,680 1,520 1,053,168 36,893 1,194,848 38,413 
Mortgage-backed251,861 2,265 839,061 130,415 1,090,922 132,680 
Asset-backed644,346 1,643 503,876 15,600 1,148,222 17,243 
Corporate494,240 4,308 1,786,925 58,671 2,281,165 62,979 
Foreign government666,054 9,770 285,640 168,090 951,694 177,860 
Fixed maturity securities$2,988,258 $28,408 $4,652,566 $415,924 $7,640,824 $444,332 
    Substantially all of the securities in an unrealized loss position are rated investment grade, except for the securities in the foreign government classification. A significant amount of the unrealized loss on foreign government securities is the result of changes in currency exchange rates. 
    A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2026 is presented in the table below:
($ in thousands)Number of
Securities		Aggregate
Fair Value		Gross
Unrealized Loss
Foreign government59 $159,082 $174,727 
State and municipal5 29,106 894 
Corporate15 22,759 950 
Mortgage-backed14 1,897 116 
Total93 $212,844 $176,687 
    
For fixed maturity securities that management does not intend to sell or to be required to sell, the portion of the decline in value that is considered to be due to credit factors is recognized in earnings, and the portion of the decline in value that is considered to be due to non-credit factors is recognized in other comprehensive income (loss).
     The Company has evaluated its fixed maturity securities in an unrealized loss position and believes the unrealized losses are due primarily to temporary market and sector-related factors rather than to issuer-specific factors. None of these securities are delinquent or in default under financial covenants. Based on its assessment of these issuers, the Company expects them to continue to meet their contractual payment obligations as they become due.
v3.26.1
Fair Value Measurements
 3 Months Ended
Mar. 31, 2026
Fair Value Disclosures [Abstract]  
Fair Value Measurements Fair Value Measurements
    The Company’s fixed maturity available for sale securities, equity securities and its arbitrage trading account securities are carried at fair value. Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels, as follows:
Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.
Level 2 - Quoted prices for similar assets or valuations based on inputs that are observable.
Level 3 - Estimates of fair value based on internal pricing methodologies using unobservable inputs. Unobservable inputs are only used to measure fair value to the extent that observable inputs are not available.
    Substantially all of the Company’s fixed maturity securities were priced by independent pricing services (generally one
U.S. pricing service plus additional pricing services with respect to a limited number of foreign securities held by the Company). The prices provided by the independent pricing services are estimated based on observable market data in active markets utilizing pricing models and processes, which may include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, sector groupings, matrix pricing and reference data. The pricing services may prioritize inputs differently on any given day for any security based on market conditions, and not all inputs are available for each security evaluation on any given day. The pricing services used by the Company have indicated that they will only produce an estimate of fair value if objectively verifiable information is available. The determination of whether markets are active or inactive is based upon the volume and level of activity for a particular asset class. The Company reviews the prices provided by pricing services for reasonableness and periodically performs independent price tests of a sample of securities to ensure proper valuation.
    If prices from independent pricing services are not available for fixed maturity securities, the Company estimates the fair value. For Level 2 securities, the Company utilizes pricing models and processes which may include benchmark yields, sector groupings, matrix pricing, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, bids, offers and reference data. Where broker quotes are used, the Company generally requests two or more quotes and sets a price within the range of quotes received based on its assessment of the credibility of the quote and its own evaluation of the security. The Company generally does not adjust quotes received from brokers. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information.
    For Level 3 securities, the Company generally uses a discounted cash flow model to estimate the fair value of fixed maturity securities. The cash flow models are based upon assumptions as to prevailing credit spreads, interest rate and interest rate volatility, time to maturity and subordination levels. Projected cash flows are discounted at rates that are adjusted to reflect illiquidity, where appropriate.
    
    The following tables present the assets and liabilities measured at fair value on a recurring basis as of March 31, 2026 and December 31, 2025 by level:
(In thousands)TotalLevel 1Level 2Level 3
March 31, 2026
Assets:
Fixed maturity securities available for sale:
U.S. government and government agency$4,383,573 $— $4,383,573 $— 
State and municipal1,751,807 — 1,751,807 — 
Mortgage-backed4,720,058 — 4,720,058 — 
Asset-backed3,868,945 — 3,868,945 — 
Corporate8,776,170 — 8,756,299 19,871 
Foreign government1,976,931 — 1,976,931 — 
Total fixed maturity securities available for sale25,477,484 — 25,457,613 19,871 
Equity securities:
Common stocks849,670 846,795 772 2,103 
Preferred stocks619,981 — 611,307 8,674 
Total equity securities1,469,651 846,795 612,079 10,777 
Arbitrage trading account1,164,872 1,058,448 106,311 113 
Total$28,112,007 $1,905,243 $26,176,003 $30,761 
Liabilities:
Trading account securities sold but not yet purchased$33 $33 $— $— 
December 31, 2025
Assets:
Fixed maturity securities available for sale:
U.S. government and government agency$3,998,038 $— $3,998,038 $— 
State and municipal1,837,194 — 1,837,194 — 
Mortgage-backed4,808,478 — 4,808,478 — 
Asset-backed3,810,346 — 3,810,346 — 
Corporate8,687,411 — 8,667,410 20,001 
Foreign government1,875,589 — 1,875,589 — 
Total fixed maturity securities available for sale25,017,056 — 24,997,055 20,001 
Equity securities:
Common stocks742,113 739,186 786 2,141 
Preferred stocks616,088 — 607,414 8,674 
Total equity securities1,358,201 739,186 608,200 10,815 
Arbitrage trading account1,221,103 1,139,447 81,543 113 
Total$27,596,360 $1,878,633 $25,686,798 $30,929 
Liabilities:
Trading account securities sold but not yet purchased$66,285 $66,285 $— $— 
    The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2026 and for the year ended December 31, 2025:
(Losses) Gains Included In:
(In thousands)Beginning
Balance		(Losses) Earnings Other
Comprehensive (Losses) Income 		PurchasesSalesTransfers In / (Out)Ending
Balance
Three Months Ended March 31, 2026
Assets:
Fixed maturity securities available for sale:
Corporate$20,001 $— $(130)$— $— $— $19,871 
Total20,001 — (130)— — — 19,871 
Equity securities:
Common stocks2,141 (38)— — — — 2,103 
Preferred stocks8,674 — — — — — 8,674 
Total10,815 (38)— — — — 10,777 
Arbitrage trading account113 — — — — — 113 
Total$30,929 $(38)$(130)$— $— $— $30,761 
Year Ended December 31, 2025
Assets:
Fixed maturity securities available for sale:
Corporate$19,667 $— $334 $— $— $— $20,001 
Total19,667 — 334 — — — 20,001 
Equity securities:
Common stocks2,041 226 — — (126)— 2,141 
Preferred stocks3,674 — — 6,160 (1,160)— 8,674 
Total5,715 226 — 6,160 (1,286)— 10,815 
Arbitrage trading account3,510 1,745 — — (5,143)1 113 
Total$28,892 $1,971 $334 $6,160 $(6,429)$1 $30,929 
    For the year ended December 31, 2025, one security within the arbitrage trading account portfolio was transferred into Level 3 from Level 2 given there were no available quoted prices or observable inputs.
Fair Value of Financial Instruments
    The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments:
  March 31, 2026December 31, 2025
(In thousands)Carrying ValueFair ValueCarrying ValueFair Value
Assets:
Fixed maturity securities$25,508,409 $25,509,018 $25,047,662 $25,048,534 
Equity securities1,469,651 1,469,651 1,358,201 1,358,201 
Arbitrage trading account1,164,872 1,164,872 1,221,103 1,221,103 
Loans receivable441,160 441,236 418,913 419,074 
Cash and cash equivalents2,280,934 2,280,934 2,539,938 2,539,938 
Trading account receivables from brokers and clearing organizations8,690 8,690 11,669 11,669 
     Due from broker— — 629 629 
Liabilities:
Due to broker157,034 157,034 — — 
Trading account securities sold but not yet purchased33 33 66,285 66,285 
Senior notes and other debt1,830,328 1,417,275 1,829,198 1,440,055 
Subordinated debentures1,010,707 730,234 1,010,527 760,400 
    The estimated fair values of the Company’s fixed maturity securities, equity securities and arbitrage trading account securities are based on various valuation techniques that rely on fair value measurements as described in Note 15. The fair value of loans receivable is estimated by using current institutional purchaser yield requirements for loans with similar credit characteristics, which is considered a Level 2 input. The fair value of the senior notes and other debt and the subordinated debentures is based on spreads for similar securities, which is considered a Level 2 input.
v3.26.1
Reserves for Loss and Loss Expenses
 3 Months Ended
Mar. 31, 2026
Insurance [Abstract]  
Reserves for Loss and Loss Expenses Reserves for Loss and Loss Expenses
    The Company's reserves for losses and loss expenses are comprised of case reserves and incurred but not reported liabilities ("IBNR"). When a claim is reported, a case reserve is established for the estimated ultimate payment based upon known information about the claim. As more information about the claim becomes available over time, case reserves are adjusted up or down as appropriate. Reserves are also established on an aggregate basis to provide for IBNR liabilities and expected loss reserve development on reported claims.
    Loss reserves included in the Company’s financial statements represent management’s best estimates based upon an actuarially derived point estimate and other considerations. The Company uses a variety of actuarial techniques and methods to derive an actuarial point estimate for each operating unit. These methods include paid loss development, incurred loss development, paid and incurred Bornhuetter-Ferguson methods and frequency and severity methods. In circumstances where one actuarial method is considered more credible than the others, that method is used to set the point estimate. The actuarial point estimate may also be based on a judgmental weighting of estimates produced from each of the methods considered. Industry loss experience is used to supplement the Company’s own data in selecting “tail factors” in areas where the Company’s own data is limited. The actuarial data is analyzed by line of business, coverage and accident or policy year, as appropriate, for each operating unit.
    The establishment of the actuarially derived loss reserve point estimate also includes consideration of qualitative factors that may affect the ultimate losses. These qualitative considerations include, among others, the impact of re-underwriting initiatives, changes in the mix of business, changes in distribution sources and changes in policy terms and conditions.
    The key assumptions used to arrive at the best estimate of loss reserves are the expected loss ratios, rate of loss cost inflation, and reported and paid loss emergence patterns. Expected loss ratios represent management’s expectation of losses at the time the business is priced and written, before any actual claims experience has emerged. This expectation is a significant determinant of the estimate of loss reserves for recently written business where there is little paid or incurred loss data to consider. Expected loss ratios are generally derived from historical loss ratios adjusted for the impact of rate changes, loss cost trends and known changes in the type of risks underwritten. Expected loss ratios are estimated for each key line of business within each operating unit. Expected loss cost inflation is particularly important for the long-tail lines, such as excess casualty, and claims with a high medical component, such as workers’ compensation. Reported and paid loss emergence patterns are used to project current reported or paid loss amounts to their ultimate settlement value. Loss development factors are based on the historical emergence patterns of paid and incurred losses, and are derived from the Company’s own experience and industry data. The paid loss emergence pattern is also significant to excess and assumed workers’ compensation reserves because those reserves are discounted to their estimated present value based upon such estimated payout patterns.
    Loss frequency and severity are measures of loss activity that are considered in determining the key assumptions described in our discussion of loss and loss expense reserves, including expected loss ratios, rate of loss cost inflation and reported and paid loss emergence patterns. Loss frequency is a measure of the number of claims per unit of insured exposure, and loss severity is a measure of the average size of claims. Factors affecting loss frequency include the effectiveness of loss controls and safety programs and changes in economic activity or weather patterns. Factors affecting loss severity include changes in policy limits, retentions, rate of inflation and judicial interpretations.
    Another factor affecting estimates of loss frequency and severity is the loss reporting lag, which is the period of time between the occurrence of a loss and the date the loss is reported to the Company. The length of the loss reporting lag affects our ability to accurately predict loss frequency (loss frequencies are more predictable for lines with short reporting lags) as well as the amount of reserves needed for incurred but not reported losses (less IBNR is required for lines with short reporting lags). As a result, loss reserves for lines with short reporting lags are likely to have less variation from initial loss estimates. For lines with short reporting lags, which include commercial automobile, primary workers’ compensation, other liability (claims-made) and property business, the key assumption is the loss emergence pattern used to project ultimate loss estimates from known losses paid or reported to date. For lines of business with long reporting lags, which include other liability (occurrence), products liability, excess workers’ compensation and liability reinsurance, the key assumption is the expected loss ratio since there is often little paid or incurred loss data to consider. Historically, the Company has experienced less variation from its initial loss estimates for lines of business with short reporting lags than for lines of business with long reporting lags.
    The key assumptions used in calculating the most recent estimate of the loss reserves are reviewed each quarter and adjusted, to the extent necessary, to reflect the latest reported loss data, current trends and other factors observed.
    The table below provides a reconciliation of the beginning and ending reserve balances:
March 31,
(In thousands)20262025
Net reserves at beginning of period$18,953,674 $17,166,641 
Net provision for losses and loss expenses:
Claims occurring during the current year (1)1,922,419 1,883,708 
Increase in estimates for claims occurring in prior years (2) (3)5,435 9,604 
Loss reserve discount accretion 8,171 7,480 
Total1,936,025 1,900,792 
Net payments for claims:  
Current year118,765 127,193 
Prior years1,424,066 1,304,763 
Total1,542,831 1,431,956 
Foreign currency translation777 43,780 
Net reserves at end of period19,347,645 17,679,257 
Ceded reserves at end of period3,268,615 3,242,730 
Gross reserves at end of period$22,616,260 $20,921,987 
_______________________________________
(1) Claims occurring during the current year are net of loss reserve discounts of $17 million and $14 million for the three months ended March 31, 2026 and 2025, respectively.
(2) The change in estimates for claims occurring in prior years is net of loss reserve discount. On an undiscounted basis, the estimates for claims occurring in prior years increased by $2 million and $12 million for the three months ended March 31, 2026 and 2025, respectively.
(3) For certain retrospectively rated insurance policies and reinsurance agreements, reserve development is offset by additional or return premiums. Favorable development, net of additional and return premiums, was $1 million for both the three months ended March 31, 2026 and 2025.
During the three months ended March 31, 2026, favorable prior year development (net of additional and return premiums) of $1 million included $9 million of favorable prior year development for the Reinsurance & Monoline Excess segment partially offset by $8 million of adverse prior year development for the Insurance segment.
For the Insurance segment, the development during the first quarter of 2026 resulted primarily from favorable development for short-tail lines of business which was offset by adverse development for other liability. The favorable development for short-tail lines of business related to the 2025 accident year and resulted from favorable settlements of both catastrophe and non-catastrophe property claims below our expectations. In addition, auto physical damage experienced favorable prior year development during the first quarter of 2026, also related to favorable claim settlements from the 2025 accident year below our expectations.
The adverse other liability development was driven mainly by umbrella and excess liability claims, and to a lesser extent from the Company’s primary surplus lines casualty business. The other liability development was concentrated in accident years 2019 through 2023. The umbrella and excess liability development included a significant component stemming from underlying auto exposures. The Company believes that auto related claims are being particularly impacted by social inflation. An increase in the frequency of litigated claims is also driving up both indemnity and loss adjustment expense costs in these lines of business beyond expectations.
For the Reinsurance & Monoline Excess segment, the favorable development during the first quarter of 2026 was driven mainly by favorable development in non-proportional reinsurance assumed property, partially offset by adverse development in the non-proportional reinsurance assumed liability line of business. Similarly to the Insurance segment, the favorable property reinsurance development was driven by favorable claim settlements, below our expectations, related to the 2025 accident year. The unfavorable development for non-proportional reinsurance assumed liability was associated primarily with our U.S. assumed reinsurance businesses, and was concentrated mainly in accident years 2019 through 2023.
During the three months ended March 31, 2025, favorable prior year development (net of additional and return premiums) of $1 million included $12 million of for the Reinsurance & Monoline Excess segment partially offset by $11 million of adverse prior year development for the Insurance segment.
For the Insurance segment, the adverse development during the first quarter of 2025 was driven primarily by excess other liability, including umbrella, and was partially offset by favorable development for short-tail lines of business, including
commercial property and commercial auto physical damage. The adverse excess other liability, including umbrella, development was concentrated in accident years 2018 through 2022, and included a significant component stemming from underlying auto exposures. The Company believes that auto-related claims are being particularly impacted by social inflation, which is contributing to an increase in the frequency of large losses beyond expectations. Social inflation can include higher settlement demands from plaintiffs, use of tactics such as litigation funding by the plaintiffs’ bar, negative public sentiment towards large businesses and corporations, and erosion of tort reforms, among others. The favorable development for short-tail property lines of business during the first quarter of 2025 related to the 2024 accident year, and resulted from favorable settlements of both catastrophe and non-catastrophe claims below our expectations.
For the Reinsurance & Monoline Excess segment, the favorable development during the first quarter of 2025 was driven mainly by favorable development in non-proportional reinsurance assumed property, partially offset by adverse development in the non-proportional reinsurance assumed liability line of business. Similar to the Insurance segment, the favorable property reinsurance development was driven by favorable claim settlements, below our expectations, related to the 2024 accident year. The unfavorable development for non-proportional reinsurance assumed liability was associated primarily with our U.S. assumed reinsurance businesses, and was concentrated mainly in accident years 2018 through 2021.
v3.26.1
Fair Value Of Financial Instruments
 3 Months Ended
Mar. 31, 2026
Fair Value Disclosures [Abstract]  
Fair Value Of Financial Instruments Fair Value Measurements
    The Company’s fixed maturity available for sale securities, equity securities and its arbitrage trading account securities are carried at fair value. Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels, as follows:
Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.
Level 2 - Quoted prices for similar assets or valuations based on inputs that are observable.
Level 3 - Estimates of fair value based on internal pricing methodologies using unobservable inputs. Unobservable inputs are only used to measure fair value to the extent that observable inputs are not available.
    Substantially all of the Company’s fixed maturity securities were priced by independent pricing services (generally one
U.S. pricing service plus additional pricing services with respect to a limited number of foreign securities held by the Company). The prices provided by the independent pricing services are estimated based on observable market data in active markets utilizing pricing models and processes, which may include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, sector groupings, matrix pricing and reference data. The pricing services may prioritize inputs differently on any given day for any security based on market conditions, and not all inputs are available for each security evaluation on any given day. The pricing services used by the Company have indicated that they will only produce an estimate of fair value if objectively verifiable information is available. The determination of whether markets are active or inactive is based upon the volume and level of activity for a particular asset class. The Company reviews the prices provided by pricing services for reasonableness and periodically performs independent price tests of a sample of securities to ensure proper valuation.
    If prices from independent pricing services are not available for fixed maturity securities, the Company estimates the fair value. For Level 2 securities, the Company utilizes pricing models and processes which may include benchmark yields, sector groupings, matrix pricing, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, bids, offers and reference data. Where broker quotes are used, the Company generally requests two or more quotes and sets a price within the range of quotes received based on its assessment of the credibility of the quote and its own evaluation of the security. The Company generally does not adjust quotes received from brokers. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information.
    For Level 3 securities, the Company generally uses a discounted cash flow model to estimate the fair value of fixed maturity securities. The cash flow models are based upon assumptions as to prevailing credit spreads, interest rate and interest rate volatility, time to maturity and subordination levels. Projected cash flows are discounted at rates that are adjusted to reflect illiquidity, where appropriate.
    
    The following tables present the assets and liabilities measured at fair value on a recurring basis as of March 31, 2026 and December 31, 2025 by level:
(In thousands)TotalLevel 1Level 2Level 3
March 31, 2026
Assets:
Fixed maturity securities available for sale:
U.S. government and government agency$4,383,573 $— $4,383,573 $— 
State and municipal1,751,807 — 1,751,807 — 
Mortgage-backed4,720,058 — 4,720,058 — 
Asset-backed3,868,945 — 3,868,945 — 
Corporate8,776,170 — 8,756,299 19,871 
Foreign government1,976,931 — 1,976,931 — 
Total fixed maturity securities available for sale25,477,484 — 25,457,613 19,871 
Equity securities:
Common stocks849,670 846,795 772 2,103 
Preferred stocks619,981 — 611,307 8,674 
Total equity securities1,469,651 846,795 612,079 10,777 
Arbitrage trading account1,164,872 1,058,448 106,311 113 
Total$28,112,007 $1,905,243 $26,176,003 $30,761 
Liabilities:
Trading account securities sold but not yet purchased$33 $33 $— $— 
December 31, 2025
Assets:
Fixed maturity securities available for sale:
U.S. government and government agency$3,998,038 $— $3,998,038 $— 
State and municipal1,837,194 — 1,837,194 — 
Mortgage-backed4,808,478 — 4,808,478 — 
Asset-backed3,810,346 — 3,810,346 — 
Corporate8,687,411 — 8,667,410 20,001 
Foreign government1,875,589 — 1,875,589 — 
Total fixed maturity securities available for sale25,017,056 — 24,997,055 20,001 
Equity securities:
Common stocks742,113 739,186 786 2,141 
Preferred stocks616,088 — 607,414 8,674 
Total equity securities1,358,201 739,186 608,200 10,815 
Arbitrage trading account1,221,103 1,139,447 81,543 113 
Total$27,596,360 $1,878,633 $25,686,798 $30,929 
Liabilities:
Trading account securities sold but not yet purchased$66,285 $66,285 $— $— 
    The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2026 and for the year ended December 31, 2025:
(Losses) Gains Included In:
(In thousands)Beginning
Balance		(Losses) Earnings Other
Comprehensive (Losses) Income 		PurchasesSalesTransfers In / (Out)Ending
Balance
Three Months Ended March 31, 2026
Assets:
Fixed maturity securities available for sale:
Corporate$20,001 $— $(130)$— $— $— $19,871 
Total20,001 — (130)— — — 19,871 
Equity securities:
Common stocks2,141 (38)— — — — 2,103 
Preferred stocks8,674 — — — — — 8,674 
Total10,815 (38)— — — — 10,777 
Arbitrage trading account113 — — — — — 113 
Total$30,929 $(38)$(130)$— $— $— $30,761 
Year Ended December 31, 2025
Assets:
Fixed maturity securities available for sale:
Corporate$19,667 $— $334 $— $— $— $20,001 
Total19,667 — 334 — — — 20,001 
Equity securities:
Common stocks2,041 226 — — (126)— 2,141 
Preferred stocks3,674 — — 6,160 (1,160)— 8,674 
Total5,715 226 — 6,160 (1,286)— 10,815 
Arbitrage trading account3,510 1,745 — — (5,143)1 113 
Total$28,892 $1,971 $334 $6,160 $(6,429)$1 $30,929 
    For the year ended December 31, 2025, one security within the arbitrage trading account portfolio was transferred into Level 3 from Level 2 given there were no available quoted prices or observable inputs.
Fair Value of Financial Instruments
    The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments:
  March 31, 2026December 31, 2025
(In thousands)Carrying ValueFair ValueCarrying ValueFair Value
Assets:
Fixed maturity securities$25,508,409 $25,509,018 $25,047,662 $25,048,534 
Equity securities1,469,651 1,469,651 1,358,201 1,358,201 
Arbitrage trading account1,164,872 1,164,872 1,221,103 1,221,103 
Loans receivable441,160 441,236 418,913 419,074 
Cash and cash equivalents2,280,934 2,280,934 2,539,938 2,539,938 
Trading account receivables from brokers and clearing organizations8,690 8,690 11,669 11,669 
     Due from broker— — 629 629 
Liabilities:
Due to broker157,034 157,034 — — 
Trading account securities sold but not yet purchased33 33 66,285 66,285 
Senior notes and other debt1,830,328 1,417,275 1,829,198 1,440,055 
Subordinated debentures1,010,707 730,234 1,010,527 760,400 
    The estimated fair values of the Company’s fixed maturity securities, equity securities and arbitrage trading account securities are based on various valuation techniques that rely on fair value measurements as described in Note 15. The fair value of loans receivable is estimated by using current institutional purchaser yield requirements for loans with similar credit characteristics, which is considered a Level 2 input. The fair value of the senior notes and other debt and the subordinated debentures is based on spreads for similar securities, which is considered a Level 2 input.
v3.26.1
Premiums and Reinsurance Related Information
 3 Months Ended
Mar. 31, 2026
Insurance [Abstract]  
Premiums and Reinsurance Related Information Premiums and Reinsurance Related Information
The following is a summary of insurance and reinsurance financial information:
For the Three Months
Ended March 31,
(In thousands)20262025
Written premiums:
Direct$3,471,186 $3,310,893 
Assumed314,580 373,046 
Ceded(611,421)(550,637)
Total net premiums written$3,174,345 $3,133,302 
Earned premiums:
Direct$3,424,142 $3,233,843 
Assumed314,934 339,596 
Ceded(623,904)(561,058)
Total net premiums earned$3,115,172 $3,012,381 
Ceded losses and loss expenses incurred$357,740 $314,252 
Ceded commissions earned$152,948 $139,604 
    The following table presents the rollforward of the allowance for expected credit losses for premiums and fees receivable for the three months ended March 31, 2026 and 2025:
(In thousands)20262025
Allowance for expected credit losses, beginning of period$42,006 $39,884 
Change in expected credit losses124 (1,023)
Allowance for expected credit losses, end of period$42,130 $38,861 
The Company reinsures a portion of its insurance exposures in order to reduce its net liability on individual risks and catastrophe losses. The Company also cedes premiums to state assigned risk plans and captive insurance companies. Estimated amounts due from reinsurers are reported net of an allowance for expected credit losses.
The following table presents the rollforward of the allowance for expected credit losses associated with due from reinsurers for the three months ended March 31, 2026 and 2025:
(In thousands)20262025
Allowance for expected credit losses, beginning of period$6,378 $8,350 
Change in expected credit losses(1,406)(1,266)
Allowance for expected credit losses, end of period$4,972 $7,084 
v3.26.1
Restricted Stock Units
 3 Months Ended
Mar. 31, 2026
Share-Based Payment Arrangement [Abstract]  
Restricted Stock Units Restricted Stock Units
    Pursuant to its stock incentive plan, the Company may issue restricted stock units ("RSUs") to employees of the Company and its subsidiaries. The RSUs generally vest three to five years from the award date and are subject to other vesting and forfeiture provisions contained in the award agreement. RSUs are expensed pro-ratably over the vesting period. RSU expenses were $13 million and $12 million for the three months ended March 31, 2026 and 2025, respectively. A summary of RSUs issued in the three months ended March 31, 2026 and 2025 follows:
($ in thousands)
UnitsFair Value
20266,045 $432 
202520,647$1,210 
v3.26.1
Litigation and Contingent Liabilities
 3 Months Ended
Mar. 31, 2026
Commitments and Contingencies Disclosure [Abstract]  
Litigation and Contingent Liabilities Litigation and Contingent Liabilities
    In the ordinary course of business, the Company is subject to disputes, litigation and arbitration arising from its insurance and reinsurance businesses. These matters are generally related to insurance and reinsurance claims and are considered in the establishment of loss and loss expense reserves. In addition, the Company may also become involved in legal actions which seek extra-contractual damages, punitive damages or penalties, including claims alleging bad faith in handling of insurance claims. The Company expects its ultimate liability with respect to such matters will not be material to its financial condition. However, adverse outcomes on such matters are possible, from time to time, and could be material to the Company’s results of operations in any particular financial reporting period.
On December 22, 2023, one of the Company’s subsidiaries filed a lawsuit against certain reinsurers to recover in excess of $90 million in respect of certain losses paid to its policyholders under certain event cancellation and related insurance policies. On April 23, 2026, the court issued a judgment that principally resolved the lawsuit in favor of the Company's subsidiary. The amount of the award for such subsidiary will be determined by the court. The Company believes that the award, in any case, will not be material to the Company’s financial condition.
v3.26.1
Leases
 3 Months Ended
Mar. 31, 2026
Leases [Abstract]  
Leases Leases
    Lessees are required to recognize a right-of-use asset and a lease liability for leases with terms of more than 12 months on the balance sheet. All leases disclosed within this footnote are classified as operating leases. Recognized right-of-use asset and lease liability are reported within other assets and other liabilities, respectively, in the consolidated balance sheet. Lease expense is reported in other operating costs and expenses in the consolidated statement of income and accounted for on a straight-line basis over the lease term.
    To determine the discount rate used to calculate present value of future minimum lease payments, the Company uses its incremental borrowing rate during the lease commencement period in line with the respective lease duration. In certain cases, the Company has the option to renew the lease. Lease renewal future payments are included in the present value of the future minimum lease payments when the Company determines it is reasonably certain to renew.
The main leases entered into by the Company are for office space used by the Company’s businesses across the world. Additionally, the Company, to a lesser extent, has equipment leases mainly for office equipment. Further information relating to operating lease expense and other operating lease information are as follows:
 For the Three Months Ended
March 31,
(In thousands)20262025
Leases:
Lease cost$13,915 $12,778 
Cash paid for amounts included in the measurement of lease liabilities reported in operating cash flows12,097 13,482 
Right-of-use assets obtained in exchange for new lease liabilities3,760 13,210 

As of March 31,
($ in thousands)20262025
Right-of-use assets$215,547$185,373
Lease liabilities$255,715$222,855
Weighted-average remaining lease term7.0 years7.2 years
Weighted-average discount rate6.00 %5.67 %
Contractual maturities of the Company’s future minimum lease payments are as follows:
(In thousands)March 31, 2026
Contractual Maturities:
2026$40,758 
202748,450 
202846,802 
202942,731 
203037,907 
Thereafter99,086 
Total undiscounted future minimum lease payments315,734 
Less: Discount impact60,019 
Total lease liability$255,715 
v3.26.1
Business Segments
 3 Months Ended
Mar. 31, 2026
Segment Reporting [Abstract]  
Business Segments Business Segments
    The Company’s reportable segments include the following two business segments, plus a corporate segment:
•Insurance - predominantly commercial insurance business, including excess and surplus lines, admitted lines and specialty personal lines throughout the United States, as well as insurance business in Asia, Australia, Canada, Continental Europe, Mexico, Scandinavia, South America and the United Kingdom.
•Reinsurance & Monoline Excess - reinsurance business on a facultative and treaty basis, primarily in the United States, the United Kingdom, Continental Europe, Australia, the Asia-Pacific Region and South Africa, as well as operations that solely retain risk on an excess basis and certain program management business.
The Company's chief operating decision maker ("CODM") is the President and Chief Executive Officer. The CODM assesses performance, makes decisions and allocates resources for each of the three reportable segments based on their contribution towards the Company's profitability and balance sheet strength. Certain key metrics such as combined ratio and return on allocated capital for the Insurance and Reinsurance & Monoline Excess segments, as well as Corporate segment expenditures, are examples of key components of the assessment, decision-making and resource-allocation process.
    The accounting policies of the segments are the same as those described in the summary of significant accounting policies. Income tax expense and benefits are calculated based upon the Company's overall effective tax rate.
    Summary financial information about the Company's reporting segments is presented in the following tables. Income (loss) before income taxes by segment includes allocated investment income. Identifiable assets by segment are those assets used in or allocated to the operation of each segment.
  RevenuesExpenses  
(In thousands)Earned
Premiums (1)		Investment
Income		OtherTotal (2)Losses and Loss ExpensesPolicy Acquisition and Insurance Operating ExpensesOtherTotalPre-Tax Income (Loss)Net Income (Loss) to Common Stockholders
Three months ended March 31, 2026
Insurance$2,765,492 $311,241 $9,843 $3,086,576 $1,766,968 $783,419 $11,526 $2,561,913 $524,663 $433,467 
Reinsurance & Monoline Excess349,680 67,849 — 417,529 169,057 105,766 — 274,823 142,706 122,367 
Corporate, other and eliminations (3)— 25,243 176,761 202,004 — — 237,500 237,500 (35,496)(28,224)
Net investment losses— — (15,775)(15,775)— — — — (15,775)(12,394)
Total$3,115,172 $404,333 $170,829 $3,690,334 $1,936,025 $889,185 $249,026 $3,074,236 $616,098 $515,216 
Three months ended March 31, 2025
Insurance$2,642,507 $291,248 $9,952 $2,943,707 $1,687,453 $735,661 $11,088 $2,434,202 $509,505 $393,122 
Reinsurance & Monoline Excess369,874 66,430 — 436,304 213,339 102,585 — 315,924 120,380 95,843 
Corporate, other and eliminations (3)— 2,614 148,419 151,033 — — 258,667 258,667 (107,634)(84,221)
Net investment gains— — 16,355 16,355 — — — — 16,355 12,827 
Total$3,012,381 $360,292 $174,726 $3,547,399 $1,900,792 $838,246 $269,755 $3,008,793 $538,606 $417,571 
Identifiable Assets
(In thousands)March 31,
2026		December 31,
2025
Insurance$35,954,379 $35,686,306 
Reinsurance & Monoline Excess5,777,792 5,891,538 
Corporate, other and eliminations (3)2,583,382 2,348,999 
Consolidated$44,315,553 $43,926,843 
_________________
(1) Certain amounts included in earned premiums of each segment are related to inter-segment transactions.
(2) Revenues for Insurance from foreign operations for the three months ended March 31, 2026 and 2025 were $376 million and $333 million, respectively. Revenues for Reinsurance & Monoline Excess from foreign operations for the three months ended March 31, 2026 and 2025 were $113 million and $130 million, respectively.
(3) Corporate, other and eliminations represent corporate revenues and expenses and certain other items that are not allocated to business segments.
    Net premiums earned by major line of business are as follows:
 For the Three Months
Ended March 31,
(In thousands)20262025
Insurance:
Other liability$1,097,841 $1,072,728 
Short-tail lines (1)652,523 596,109 
Auto413,492 389,949 
Workers' compensation313,742 311,028 
Professional liability287,894 272,693 
Total Insurance2,765,492 2,642,507 
Reinsurance & Monoline Excess:
Casualty (2)171,719 181,767 
Property (2)101,852 120,843 
Monoline excess (3)76,109 67,264 
Total Reinsurance & Monoline Excess349,680 369,874 
Total$3,115,172 $3,012,381 
______________
(1) Short-tail lines include commercial multi-peril (non-liability), inland marine, accident and health, fidelity and surety, boiler and machinery, high net worth homeowners and other lines.
(2) Includes reinsurance casualty and property and certain program management business.
(3) Monoline excess includes operations that solely retain risk on an excess basis.
v3.26.1
Related-Party Transactions
 3 Months Ended
Mar. 31, 2026
Related Party Transactions [Abstract]  
Related-Party Transactions Related-Party Transactions
Lifson Re
Lifson Re, a Bermuda reinsurance company, participated on a fully collateralized basis in a majority of the Company’s reinsurance placements, with a 30% share of the amounts placed commencing on July 1, 2022, which was increased to 32.5% effective January 1, 2025. This pertains to all traditional reinsurance/retrocessional placements for both property and casualty business where there is more than one open market reinsurer participating. Lifson Re is currently capitalized with $418 million from a small group of sophisticated global investors with long-term investment horizons, including a minority participation by the Company (which is included in Note 10, Investment Funds, within Financial services).
Transactions between the Company and Lifson Re were as follows:

(In thousands)
Consolidated statements of incomeMarch 31,
2026		March 31,
2025
Ceded written premiums$118,517 $106,137 
Ceded commissions and brokerage33,925 30,424 
As of
Consolidated balance sheetsMarch 31,
2026		December 31,
2025
Due from reinsurers$561,264 $537,366 
Due to reinsurers101,091 118,788 

The Company earned certain management and performance fees from Lifson Re of $3 million and $1 million for the three months ended March 31, 2026 and 2025, respectively.

Mitsui Sumitomo Insurance Co., Ltd.
Pursuant to an arrangement (“the Framework Agreement”) entered between Mitsui Sumitomo Insurance Co., Ltd. (“MSI”) and a company owned by members of the Berkley family and trusts for their benefit (collectively, the “Berkley Family”), as of March 31, 2026, MSI owned 15.8% of the Company’s outstanding common stock excluding shares held in a deferred compensation grantor trust. In addition, pursuant to the Framework Agreement, the Berkley Family recommended to the Company’s Board of Directors (the “Board”) that MSI’s designee be nominated to stand for election to the Board at the Company’s 2026 annual stockholders meeting. Upon recommendation of the Board’s Nominating and Corporate Governance Committee, the Board approved MSI’s designee standing for election.
In the normal course of its operations, the Company from time to time enters into reinsurance transactions with MSI or one of its affiliates (including its Lloyd’s of London operations), including the following:
•During the three months ended March 31, 2026, the Company ceded written premiums and had commissions with MSI or one of its affiliates of $15 million and $3 million, respectively. As of March 31, 2026, in connection with insurance ceded to MSI and its affiliates, the Company had amounts due from and due to reinsurers of $61 million and $11 million, respectively.
•During the three months ended March 31, 2026, the Company assumed written premiums from MSI or one of its affiliates of $5 million. As of March 31, 2026, in connection with insurance assumed from MSI and its affiliates, the Company had premiums receivable and due to reinsured amounts of $5 million and $11 million, respectively.
MSI has a minority investment in Lifson Re.
The Lifson Re and MSI transactions discussed above were entered into at arm's-length.
v3.26.1
Insider Trading Arrangements
 3 Months Ended
Mar. 31, 2026
Trading Arrangements, by Individual  
Rule 10b5-1 Arrangement Adopted false
Non-Rule 10b5-1 Arrangement Adopted false
Rule 10b5-1 Arrangement Terminated false
Non-Rule 10b5-1 Arrangement Terminated false
v3.26.1
Recent Accounting Pronouncements and Accounting Policies (Policies)
 3 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
Per Share Data Per Share Data
    The Company presents both basic and diluted net income per share (“EPS”) amounts. Basic EPS is calculated by dividing net income by the weighted average number of common shares outstanding during the period (including 17,378,810 and 17,659,297 common shares held in a grantor trust as of March 31, 2026 and 2025, respectively). The common shares held in the grantor trust are designated for delivery upon the settlement of restricted stock units ("RSUs") that are vested but mandatorily deferred. Accordingly, such shares deliverable under vested RSUs do not affect diluted shares outstanding since the shares are already included in basic shares outstanding (which includes the shares in the grantor trust referenced above). Diluted EPS is based upon the weighted average number of basic and common equivalent shares outstanding during the period and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect.
    The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows:
For the Three Months
Ended March 31,
(In thousands)20262025
Basic392,264 396,929 
Diluted394,779 399,825 
Recent Accounting Pronouncements Recent Accounting Pronouncements and Accounting Policies
Recently adopted accounting pronouncements:
    All accounting and reporting standards that became effective in 2026 were either not applicable to the Company or their adoption did not have a material impact on the Company.
Accounting and reporting standards that are not yet effective:

    In November 2024, the Financial Accounting Standards Board issued Accounting Standards Update 2024-03, Disaggregation of Income Statement Expenses, addressing investor requests for more transparent information. The guidance requires disclosure of specified information about certain costs and expenses in the notes to the financial statements. The guidance is effective for annual periods beginning after December 15, 2026, and interim reporting periods beginning after December 15, 2027. Prospective application is required, with retrospective application permitted. The Company will adopt this guidance for the year ended December 31, 2027 and the resulting impact will be disclosure only.
All other recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.
v3.26.1
Per Share Data (Tables)
 3 Months Ended
Mar. 31, 2026
Earnings Per Share [Abstract]  
Weighted average number of common shares The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows:
For the Three Months
Ended March 31,
(In thousands)20262025
Basic392,264 396,929 
Diluted394,779 399,825 
v3.26.1
Consolidated Statements of Comprehensive Income (Loss) (Tables)
 3 Months Ended
Mar. 31, 2026
Equity [Abstract]  
Components of changes in accumulated other comprehensive income (loss) The following tables present the components of the changes in accumulated other comprehensive (loss) income ("AOCI"):
(In thousands)Unrealized Investment (Losses) Gains Currency Translation AdjustmentsAccumulated Other Comprehensive (Loss) Income
As of and for the three months ended March 31, 2026
Changes in AOCI
Beginning of period$(124,680)$(326,417)$(451,097)
Other comprehensive loss before reclassifications(148,410)(5,224)(153,634)
Amounts reclassified from AOCI3,454 — 3,454 
Other comprehensive loss(144,956)(5,224)(150,180)
Unrealized investment loss related to noncontrolling interest— — — 
End of period$(269,636)$(331,641)$(601,277)
Amounts reclassified from AOCI
Pre-tax$4,372 (1)$— $4,372 
Tax effect (918)(2)— (918)
After-tax amounts reclassified$3,454 $— $3,454 
Other comprehensive loss
Pre-tax$(185,971)$(5,224)$(191,195)
Tax effect41,015 — 41,015 
Other comprehensive loss$(144,956)$(5,224)$(150,180)

As of and for the three months ended March 31, 2025
Changes in AOCI
Beginning of period$(517,170)$(417,099)$(934,269)
Other comprehensive income before reclassifications144,102 23,930 168,032 
Amounts reclassified from AOCI4,171 — 4,171 
Other comprehensive income148,273 23,930 172,203 
Unrealized investment loss related to noncontrolling interest(1)— (1)
End of period$(368,898)$(393,169)$(762,067)
Amounts reclassified from AOCI
Pre-tax$5,280 (1)$— $5,280 
Tax effect (1,109)(2)— (1,109)
After-tax amounts reclassified$4,171 $— $4,171 
Other comprehensive income
Pre-tax$185,855 $23,930 $209,785 
Tax effect(37,582)— (37,582)
Other comprehensive income$148,273 $23,930 $172,203 
____________
(1) Net investment (losses) gains in the consolidated statements of income.
(2) Income tax expense in the consolidated statements of income.
v3.26.1
Investments in Fixed Maturity Securities (Tables)
 3 Months Ended
Mar. 31, 2026
Investments, Debt and Equity Securities [Abstract]  
Schedule of investments in fixed maturity securities At March 31, 2026 and December 31, 2025, investments in fixed maturity securities were as follows:
 
(In thousands)Amortized
Cost		Allowance for Expected Credit Losses (1)Gross UnrealizedFair
Value		Carrying
Value
GainsLosses
March 31, 2026
Held to maturity:
State and municipal$29,182 $— $552 $— $29,734 $29,182 
Residential mortgage-backed1,743 — 57 — 1,800 1,743 
Total held to maturity30,925 — 609 — 31,534 30,925 
Available for sale:
U.S. government and government agency4,378,606 — 37,479 (32,512)4,383,573 4,383,573 
State and municipal:
Special revenue1,130,177 — 5,252 (27,159)1,108,270 1,108,270 
State general obligation201,814 — 2,287 (3,804)200,297 200,297 
Pre-refunded73,923 — 721 (32)74,612 74,612 
Corporate backed159,306 — 1,261 (3,374)157,193 157,193 
Local general obligation213,685 — 969 (3,219)211,435 211,435 
Total state and municipal1,778,905 — 10,490 (37,588)1,751,807 1,751,807 
Mortgage-backed:
Residential4,592,286 (77)44,169 (138,303)4,498,075 4,498,075 
Commercial218,847 — 3,172 (36)221,983 221,983 
Total mortgage-backed4,811,133 (77)47,341 (138,339)4,720,058 4,720,058 
Asset-backed3,881,752 (229)10,025 (22,603)3,868,945 3,868,945 
Corporate:
Industrial3,514,642 — 36,565 (39,478)3,511,729 3,511,729 
Financial3,526,804 — 34,606 (26,851)3,534,559 3,534,559 
Utilities1,521,021 — 12,721 (14,083)1,519,659 1,519,659 
Other209,346 — 1,365 (488)210,223 210,223 
Total corporate8,771,813 — 85,257 (80,900)8,776,170 8,776,170 
Foreign government2,161,693 — 16,184 (200,946)1,976,931 1,976,931 
Total available for sale25,783,902 (306)206,776 (512,888)25,477,484 25,477,484 
Total investments in fixed maturity securities$25,814,827 $(306)$207,385 $(512,888)$25,509,018 $25,508,409 
____________
(1) Represents the amount of impairment that has resulted from credit-related factors. The change in the allowance for expected credit losses is recognized in the consolidated statements of income. Amount excludes unrealized losses relating to non-credit factors.
(In thousands)Amortized
Cost		Allowance for Expected Credit Losses (1)Gross UnrealizedFair
Value		Carrying
Value
GainsLosses
December 31, 2025
Held to maturity:
State and municipal$28,777 $(9)$796 $— $29,564 $28,768 
Residential mortgage-backed1,838 — 76 — 1,914 1,838 
Total held to maturity30,615 (9)872 — 31,478 30,606 
Available for sale:
U.S. government and government agency3,964,375 — 48,820 (15,157)3,998,038 3,998,038 
State and municipal:
Special revenue1,206,387 — 6,002 (27,943)1,184,446 1,184,446 
State general obligation203,543 — 3,465 (3,848)203,160 203,160 
Pre-refunded74,276 — 619 (111)74,784 74,784 
Corporate backed159,876 — 1,958 (3,459)158,375 158,375 
Local general obligation218,022 — 1,459 (3,052)216,429 216,429 
Total state and municipal1,862,104 — 13,503 (38,413)1,837,194 1,837,194 
Mortgage-backed:
Residential4,584,970 (65)71,048 (132,645)4,523,308 4,523,308 
Commercial281,573 — 3,632 (35)285,170 285,170 
Total mortgage-backed4,866,543 (65)74,680 (132,680)4,808,478 4,808,478 
Asset-backed3,807,393 — 20,196 (17,243)3,810,346 3,810,346 
Corporate:
Industrial3,627,567 — 57,466 (36,499)3,648,534 3,648,534 
Financial3,438,348 — 61,180 (16,460)3,483,068 3,483,068 
Utilities1,300,506 — 22,593 (8,878)1,314,221 1,314,221 
Other240,374 — 2,356 (1,142)241,588 241,588 
Total corporate8,606,795 — 143,595 (62,979)8,687,411 8,687,411 
Foreign government2,032,543 — 20,906 (177,860)1,875,589 1,875,589 
Total available for sale25,139,753 (65)321,700 (444,332)25,017,056 25,017,056 
Total investments in fixed maturity securities$25,170,368 $(74)$322,572 $(444,332)$25,048,534 $25,047,662 
Debt Securities, Held-to-maturity, Allowance for Credit Loss
The following table presents the rollforward of the allowance for expected credit losses for held to maturity securities for the three months ended March 31, 2026 and 2025:
(In thousands)20262025
Balance, beginning of period$9 $25 
Provision for expected credit losses(9)(5)
Balance, end of period$— $20 
Debt Securities, Available-for-sale, Allowance for Credit Loss
The following table presents the rollforward of the allowance for expected credit losses for available for sale securities for the three months ended March 31, 2026 and 2025:
20262025
(In thousands)Foreign GovernmentMortgage-backedAsset-backedState and MunicipalTotalForeign GovernmentMortgage-backedAsset-backedState and MunicipalTotal
Balance, beginning of period$— $65 $— $— $65 $216 $430 $— $— $646 
Change on securities for which credit losses were not previously recorded— — 229 — 229 — — — 10 10 
Change on securities for which credit losses were previously recorded— 12 — — 12 107 (430)— — (323)
Balance, end of period$— $77 $229 $— $306 $323 $— $— $10 $333 
During the three months ended March 31, 2026, the Company increased the allowance for expected credit losses for available for sale securities primarily due to a decrease in the fair value of one investment in the asset-backed category. During the three months ended March 31, 2025, the Company decreased the allowance for expected credit losses for available for sale securities primarily due to improved pricing related to mortgage-backed securities.
Amortized cost and fair value of fixed maturity securities by contractual maturity
The amortized cost and fair value of fixed maturity securities at March 31, 2026, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations.  
(In thousands)Amortized
Cost 		Fair
Value
Due in one year or less$1,859,542 $1,811,447 
Due after one year through five years7,947,108 7,814,089 
Due after five years through ten years3,963,797 3,959,533 
Due after ten years7,231,504 7,202,091 
Mortgage-backed securities4,812,876 4,721,858 
Total$25,814,827 $25,509,018 
________________
v3.26.1
Investments in Equity Securities (Tables)
 3 Months Ended
Mar. 31, 2026
Equity Securities  
Debt Securities, Available-for-sale [Line Items]  
Schedule of Investments in Equity Securities At March 31, 2026 and December 31, 2025, investments in equity securities were as follows:
 
(In thousands)CostGross UnrealizedFair
Value		Carrying
Value
GainsLosses
March 31, 2026
Common stocks$602,744 $255,501 $(8,575)$849,670 $849,670 
Preferred stocks513,249 112,647 (5,915)619,981 619,981 
Total$1,115,993 $368,148 $(14,490)$1,469,651 $1,469,651 
December 31, 2025
Common stocks$566,577 $181,120 $(5,584)$742,113 $742,113 
Preferred stocks433,472 187,891 (5,275)616,088 616,088 
Total$1,000,049 $369,011 $(10,859)$1,358,201 $1,358,201 
v3.26.1
Net Investment Income (Tables)
 3 Months Ended
Mar. 31, 2026
Net Investment Income [Abstract]  
Schedule of Net Investment Income Net investment income consisted of the following: 
 For the Three Months
Ended March 31,
(In thousands)20262025
Investment income (loss) earned on:
Fixed maturity securities, including cash and cash equivalents and loans receivable$346,527 $313,788 
Investment funds39,529 27,023 
Equity securities15,819 10,641 
Arbitrage trading account (1)10,313 16,329 
Real estate(4,933)(4,017)
Gross investment income407,255 363,764 
Investment expense(2,922)(3,472)
Net investment income$404,333 $360,292 
(1) Net investment income includes earnings from trading account receivables from brokers and clearing organizations.
v3.26.1
Investment Funds (Tables)
 3 Months Ended
Mar. 31, 2026
Equity Method Investments and Joint Ventures [Abstract]  
Schedule of Investment Funds Investment funds consisted of the following:
Carrying Value as of Income (Loss) from
Investment Funds
March 31,December 31,For the Three Months
Ended March 31,
(In thousands)2026202520262025
Financial services (1)$365,731 $360,320 $7,402 $7,114 
Transportation275,546 272,775 8,660 8,615 
Real Estate157,089 163,098 8,016 4,965 
Infrastructure176,316 169,847 5,792 3,502 
Energy43,565 41,966 2,433 (2,102)
Other funds379,775 353,796 7,226 4,929 
Total$1,398,022 $1,361,802 $39,529 $27,023 
(1) Includes the Company's minority investment in Lifson Re (see Note 23 Related-Party Transactions).
v3.26.1
Real Estate (Tables)
 3 Months Ended
Mar. 31, 2026
Real Estate [Abstract]  
Schedule of Real Estate Investments Investment in real estate represents directly owned property held for investment, as follows:
Carrying Value
March 31,December 31,
(In thousands)20262025
Properties in operation$1,075,345 $1,051,455 
Properties under development228,396 228,293 
Total$1,303,741 $1,279,748 
v3.26.1
Loans Receivable Loans Receivable (Tables)
 3 Months Ended
Mar. 31, 2026
Receivables [Abstract]  
Schedule of Loans Receivable
At March 31, 2026 and December 31, 2025, loans receivable were as follows:
(In thousands)March 31,
2026		December 31,
2025
Amortized cost (net of allowance for expected credit losses):
Real estate loans$441,160 $418,913 
Fair value:
Real estate loans$441,236 $419,074 
Financing Receivable, Allowance for Credit Loss
The following table presents the rollforward of the allowance for expected credit losses for loans receivable for the three months ended March 31, 2026 and 2025:
20262025
(In thousands)Real Estate LoansCommercial LoansTotalReal Estate LoansCommercial LoansTotal
Balance, beginning of period$161 $— $161 $1,088 $26 $1,114 
Change in expected credit losses(86)— (86)(312)(14)(326)
Balance, end of period$75 $— $75 $776 $12 $788 
During the three months ended March 31, 2026 and 2025, the Company decreased the allowance for expected credit losses due to a decrease in the weighted average life of the remaining loan portfolio.
v3.26.1
Net Investment (Losses) Gains (Tables)
 3 Months Ended
Mar. 31, 2026
Realized and Unrealized Investment Gains (Losses) [Abstract]  
Realized And Unrealized Investment Gains (Losses) Net investment (losses) gains were as follows:
For the Three Months
Ended March 31,
(In thousands)20262025
Net investment (losses) gains:
Fixed maturity securities:
Gains$5,148 $2,632 
Losses(6,537)(2,712)
Equity securities (1):
Net realized gains (losses) on investment sales 1 (2,595)
Change in unrealized (losses) gains (4,494)19,947 
Investment funds173 14 
Real estate (7,298)3,943 
Loans receivable131 — 
Other(2,753)(5,518)
Net realized and unrealized (losses) gains on investments in earnings before allowance for expected credit losses(15,629)15,711 
Change in allowance for expected credit losses on investments:
Fixed maturity securities(232)318 
Loans receivable86 326 
Change in allowance for expected credit losses on investments(146)644 
Net investment (losses) gains(15,775)16,355 
Income tax benefit (expense)3,381 (3,528)
After-tax net investment (losses) gains$(12,394)$12,827 
Change in unrealized investment (losses) gains on available for sale securities:
Fixed maturity securities without allowance for expected credit losses$(183,478)$183,987 
Fixed maturity securities with allowance for expected credit losses(2)(551)
Investment funds(2,519)2,496 
Other28 (77)
Total change in unrealized investment (losses) gains(185,971)185,855 
Income tax benefit (expense)41,015 (37,582)
Noncontrolling interests— (1)
After-tax change in unrealized investment (losses) gains of available for sale securities$(144,956)$148,272 
______________________
(1) The net realized gains or losses on investment sales represent the total gains or losses from the purchase dates of the equity securities. The change in unrealized gains (losses) consists of two components: (i) the reversal of the gain or loss recognized in previous periods on equity securities sold and (ii) the change in unrealized gain or loss resulting from mark-to-market adjustments on equity securities still held.
v3.26.1
Fixed Maturity Securities In An Unrealized Loss Position (Tables)
 3 Months Ended
Mar. 31, 2026
Investments, Debt and Equity Securities [Abstract]  
Securities in an unrealized loss position The following tables summarize all fixed maturity securities in an unrealized loss position at March 31, 2026 and December 31, 2025 by the length of time those securities have been continuously in an unrealized loss position:
  Less Than 12 Months12 Months or GreaterTotal
(In thousands)Fair
Value		Gross
Unrealized Losses		Fair
Value		Gross
Unrealized Losses		Fair
Value		Gross
Unrealized Losses
March 31, 2026
U.S. government and government agency$1,605,859 $27,355 $134,391 $5,157 $1,740,250 $32,512 
State and municipal272,890 2,390 919,184 35,198 1,192,074 37,588 
Mortgage-backed960,232 11,297 683,839 127,042 1,644,071 138,339 
Asset-backed1,565,320 6,184 518,177 16,419 2,083,497 22,603 
Corporate1,963,231 24,464 1,538,307 56,436 3,501,538 80,900 
Foreign government1,052,525 20,046 252,591 180,900 1,305,116 200,946 
Fixed maturity securities$7,420,057 $91,736 $4,046,489 $421,152 $11,466,546 $512,888 
December 31, 2025
U.S. government and government agency$790,077 $8,902 $183,896 $6,255 $973,973 $15,157 
State and municipal141,680 1,520 1,053,168 36,893 1,194,848 38,413 
Mortgage-backed251,861 2,265 839,061 130,415 1,090,922 132,680 
Asset-backed644,346 1,643 503,876 15,600 1,148,222 17,243 
Corporate494,240 4,308 1,786,925 58,671 2,281,165 62,979 
Foreign government666,054 9,770 285,640 168,090 951,694 177,860 
Fixed maturity securities$2,988,258 $28,408 $4,652,566 $415,924 $7,640,824 $444,332 
Non-Investment Grade Fixed Maturity Securities A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2026 is presented in the table below:
($ in thousands)Number of
Securities		Aggregate
Fair Value		Gross
Unrealized Loss
Foreign government59 $159,082 $174,727 
State and municipal5 29,106 894 
Corporate15 22,759 950 
Mortgage-backed14 1,897 116 
Total93 $212,844 $176,687 
v3.26.1
Fair Value Measurements (Tables)
 3 Months Ended
Mar. 31, 2026
Fair Value Disclosures [Abstract]  
Assets And Liabilities Measured At Fair value, On A Recurring Basis The following tables present the assets and liabilities measured at fair value on a recurring basis as of March 31, 2026 and December 31, 2025 by level:
(In thousands)TotalLevel 1Level 2Level 3
March 31, 2026
Assets:
Fixed maturity securities available for sale:
U.S. government and government agency$4,383,573 $— $4,383,573 $— 
State and municipal1,751,807 — 1,751,807 — 
Mortgage-backed4,720,058 — 4,720,058 — 
Asset-backed3,868,945 — 3,868,945 — 
Corporate8,776,170 — 8,756,299 19,871 
Foreign government1,976,931 — 1,976,931 — 
Total fixed maturity securities available for sale25,477,484 — 25,457,613 19,871 
Equity securities:
Common stocks849,670 846,795 772 2,103 
Preferred stocks619,981 — 611,307 8,674 
Total equity securities1,469,651 846,795 612,079 10,777 
Arbitrage trading account1,164,872 1,058,448 106,311 113 
Total$28,112,007 $1,905,243 $26,176,003 $30,761 
Liabilities:
Trading account securities sold but not yet purchased$33 $33 $— $— 
December 31, 2025
Assets:
Fixed maturity securities available for sale:
U.S. government and government agency$3,998,038 $— $3,998,038 $— 
State and municipal1,837,194 — 1,837,194 — 
Mortgage-backed4,808,478 — 4,808,478 — 
Asset-backed3,810,346 — 3,810,346 — 
Corporate8,687,411 — 8,667,410 20,001 
Foreign government1,875,589 — 1,875,589 — 
Total fixed maturity securities available for sale25,017,056 — 24,997,055 20,001 
Equity securities:
Common stocks742,113 739,186 786 2,141 
Preferred stocks616,088 — 607,414 8,674 
Total equity securities1,358,201 739,186 608,200 10,815 
Arbitrage trading account1,221,103 1,139,447 81,543 113 
Total$27,596,360 $1,878,633 $25,686,798 $30,929 
Liabilities:
Trading account securities sold but not yet purchased$66,285 $66,285 $— $— 
Summarize Changes In Level 3 Assets The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2026 and for the year ended December 31, 2025:
(Losses) Gains Included In:
(In thousands)Beginning
Balance		(Losses) Earnings Other
Comprehensive (Losses) Income 		PurchasesSalesTransfers In / (Out)Ending
Balance
Three Months Ended March 31, 2026
Assets:
Fixed maturity securities available for sale:
Corporate$20,001 $— $(130)$— $— $— $19,871 
Total20,001 — (130)— — — 19,871 
Equity securities:
Common stocks2,141 (38)— — — — 2,103 
Preferred stocks8,674 — — — — — 8,674 
Total10,815 (38)— — — — 10,777 
Arbitrage trading account113 — — — — — 113 
Total$30,929 $(38)$(130)$— $— $— $30,761 
Year Ended December 31, 2025
Assets:
Fixed maturity securities available for sale:
Corporate$19,667 $— $334 $— $— $— $20,001 
Total19,667 — 334 — — — 20,001 
Equity securities:
Common stocks2,041 226 — — (126)— 2,141 
Preferred stocks3,674 — — 6,160 (1,160)— 8,674 
Total5,715 226 — 6,160 (1,286)— 10,815 
Arbitrage trading account3,510 1,745 — — (5,143)1 113 
Total$28,892 $1,971 $334 $6,160 $(6,429)$1 $30,929 
v3.26.1
Reserves for Loss and Loss Expenses (Tables)
 3 Months Ended
Mar. 31, 2026
Insurance [Abstract]  
Reserve Balances The table below provides a reconciliation of the beginning and ending reserve balances:
March 31,
(In thousands)20262025
Net reserves at beginning of period$18,953,674 $17,166,641 
Net provision for losses and loss expenses:
Claims occurring during the current year (1)1,922,419 1,883,708 
Increase in estimates for claims occurring in prior years (2) (3)5,435 9,604 
Loss reserve discount accretion 8,171 7,480 
Total1,936,025 1,900,792 
Net payments for claims:  
Current year118,765 127,193 
Prior years1,424,066 1,304,763 
Total1,542,831 1,431,956 
Foreign currency translation777 43,780 
Net reserves at end of period19,347,645 17,679,257 
Ceded reserves at end of period3,268,615 3,242,730 
Gross reserves at end of period$22,616,260 $20,921,987 
_______________________________________
(1) Claims occurring during the current year are net of loss reserve discounts of $17 million and $14 million for the three months ended March 31, 2026 and 2025, respectively.
(2) The change in estimates for claims occurring in prior years is net of loss reserve discount. On an undiscounted basis, the estimates for claims occurring in prior years increased by $2 million and $12 million for the three months ended March 31, 2026 and 2025, respectively.
(3) For certain retrospectively rated insurance policies and reinsurance agreements, reserve development is offset by additional or return premiums. Favorable development, net of additional and return premiums, was $1 million for both the three months ended March 31, 2026 and 2025.
v3.26.1
Fair Value of Financial Instruments (Tables)
 3 Months Ended
Mar. 31, 2026
Fair Value Disclosures [Abstract]  
Carrying Amounts And Estimated Fair Values Of Financial Instruments The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments:
  March 31, 2026December 31, 2025
(In thousands)Carrying ValueFair ValueCarrying ValueFair Value
Assets:
Fixed maturity securities$25,508,409 $25,509,018 $25,047,662 $25,048,534 
Equity securities1,469,651 1,469,651 1,358,201 1,358,201 
Arbitrage trading account1,164,872 1,164,872 1,221,103 1,221,103 
Loans receivable441,160 441,236 418,913 419,074 
Cash and cash equivalents2,280,934 2,280,934 2,539,938 2,539,938 
Trading account receivables from brokers and clearing organizations8,690 8,690 11,669 11,669 
     Due from broker— — 629 629 
Liabilities:
Due to broker157,034 157,034 — — 
Trading account securities sold but not yet purchased33 33 66,285 66,285 
Senior notes and other debt1,830,328 1,417,275 1,829,198 1,440,055 
Subordinated debentures1,010,707 730,234 1,010,527 760,400 
v3.26.1
Premiums and Reinsurance Related Information (Tables)
 3 Months Ended
Mar. 31, 2026
Insurance [Abstract]  
Reinsurance Financial Information
The following is a summary of insurance and reinsurance financial information:
For the Three Months
Ended March 31,
(In thousands)20262025
Written premiums:
Direct$3,471,186 $3,310,893 
Assumed314,580 373,046 
Ceded(611,421)(550,637)
Total net premiums written$3,174,345 $3,133,302 
Earned premiums:
Direct$3,424,142 $3,233,843 
Assumed314,934 339,596 
Ceded(623,904)(561,058)
Total net premiums earned$3,115,172 $3,012,381 
Ceded losses and loss expenses incurred$357,740 $314,252 
Ceded commissions earned$152,948 $139,604 
Premium receivable, allowance for credit loss The following table presents the rollforward of the allowance for expected credit losses for premiums and fees receivable for the three months ended March 31, 2026 and 2025:
(In thousands)20262025
Allowance for expected credit losses, beginning of period$42,006 $39,884 
Change in expected credit losses124 (1,023)
Allowance for expected credit losses, end of period$42,130 $38,861 
Reinsurance Recoverable, Allowance for Credit Loss
The following table presents the rollforward of the allowance for expected credit losses associated with due from reinsurers for the three months ended March 31, 2026 and 2025:
(In thousands)20262025
Allowance for expected credit losses, beginning of period$6,378 $8,350 
Change in expected credit losses(1,406)(1,266)
Allowance for expected credit losses, end of period$4,972 $7,084 
v3.26.1
Restricted Stock Units (Tables)
 3 Months Ended
Mar. 31, 2026
Share-Based Payment Arrangement [Abstract]  
Summary Of Restricted Stock Units Issued A summary of RSUs issued in the three months ended March 31, 2026 and 2025 follows:
($ in thousands)
UnitsFair Value
20266,045 $432 
202520,647$1,210 
v3.26.1
Leases (Tables)
 3 Months Ended
Mar. 31, 2026
Leases [Abstract]  
Lease, Cost Further information relating to operating lease expense and other operating lease information are as follows:
 For the Three Months Ended
March 31,
(In thousands)20262025
Leases:
Lease cost$13,915 $12,778 
Cash paid for amounts included in the measurement of lease liabilities reported in operating cash flows12,097 13,482 
Right-of-use assets obtained in exchange for new lease liabilities3,760 13,210 
Supplemental Balance Sheet Information
As of March 31,
($ in thousands)20262025
Right-of-use assets$215,547$185,373
Lease liabilities$255,715$222,855
Weighted-average remaining lease term7.0 years7.2 years
Weighted-average discount rate6.00 %5.67 %
Maturities of Operating Lease Liabilities
Contractual maturities of the Company’s future minimum lease payments are as follows:
(In thousands)March 31, 2026
Contractual Maturities:
2026$40,758 
202748,450 
202846,802 
202942,731 
203037,907 
Thereafter99,086 
Total undiscounted future minimum lease payments315,734 
Less: Discount impact60,019 
Total lease liability$255,715 
v3.26.1
Business Segments (Tables)
 3 Months Ended
Mar. 31, 2026
Segment Reporting [Abstract]  
Financial Information Of Company Operating Segments
  RevenuesExpenses  
(In thousands)Earned
Premiums (1)		Investment
Income		OtherTotal (2)Losses and Loss ExpensesPolicy Acquisition and Insurance Operating ExpensesOtherTotalPre-Tax Income (Loss)Net Income (Loss) to Common Stockholders
Three months ended March 31, 2026
Insurance$2,765,492 $311,241 $9,843 $3,086,576 $1,766,968 $783,419 $11,526 $2,561,913 $524,663 $433,467 
Reinsurance & Monoline Excess349,680 67,849 — 417,529 169,057 105,766 — 274,823 142,706 122,367 
Corporate, other and eliminations (3)— 25,243 176,761 202,004 — — 237,500 237,500 (35,496)(28,224)
Net investment losses— — (15,775)(15,775)— — — — (15,775)(12,394)
Total$3,115,172 $404,333 $170,829 $3,690,334 $1,936,025 $889,185 $249,026 $3,074,236 $616,098 $515,216 
Three months ended March 31, 2025
Insurance$2,642,507 $291,248 $9,952 $2,943,707 $1,687,453 $735,661 $11,088 $2,434,202 $509,505 $393,122 
Reinsurance & Monoline Excess369,874 66,430 — 436,304 213,339 102,585 — 315,924 120,380 95,843 
Corporate, other and eliminations (3)— 2,614 148,419 151,033 — — 258,667 258,667 (107,634)(84,221)
Net investment gains— — 16,355 16,355 — — — — 16,355 12,827 
Total$3,012,381 $360,292 $174,726 $3,547,399 $1,900,792 $838,246 $269,755 $3,008,793 $538,606 $417,571 
Identifiable Assets
(In thousands)March 31,
2026		December 31,
2025
Insurance$35,954,379 $35,686,306 
Reinsurance & Monoline Excess5,777,792 5,891,538 
Corporate, other and eliminations (3)2,583,382 2,348,999 
Consolidated$44,315,553 $43,926,843 
_________________
(1) Certain amounts included in earned premiums of each segment are related to inter-segment transactions.
(2) Revenues for Insurance from foreign operations for the three months ended March 31, 2026 and 2025 were $376 million and $333 million, respectively. Revenues for Reinsurance & Monoline Excess from foreign operations for the three months ended March 31, 2026 and 2025 were $113 million and $130 million, respectively.
(3) Corporate, other and eliminations represent corporate revenues and expenses and certain other items that are not allocated to business segments
Net Premiums Earned By Major Line Of Business Net premiums earned by major line of business are as follows:
 For the Three Months
Ended March 31,
(In thousands)20262025
Insurance:
Other liability$1,097,841 $1,072,728 
Short-tail lines (1)652,523 596,109 
Auto413,492 389,949 
Workers' compensation313,742 311,028 
Professional liability287,894 272,693 
Total Insurance2,765,492 2,642,507 
Reinsurance & Monoline Excess:
Casualty (2)171,719 181,767 
Property (2)101,852 120,843 
Monoline excess (3)76,109 67,264 
Total Reinsurance & Monoline Excess349,680 369,874 
Total$3,115,172 $3,012,381 
______________
(1) Short-tail lines include commercial multi-peril (non-liability), inland marine, accident and health, fidelity and surety, boiler and machinery, high net worth homeowners and other lines.
(2) Includes reinsurance casualty and property and certain program management business.
(3) Monoline excess includes operations that solely retain risk on an excess basis.
v3.26.1
Related-Party Transactions (Tables)
 3 Months Ended
Mar. 31, 2026
Related Party Transactions [Abstract]  
Schedule of Related Party Transactions
Transactions between the Company and Lifson Re were as follows:

(In thousands)
Consolidated statements of incomeMarch 31,
2026		March 31,
2025
Ceded written premiums$118,517 $106,137 
Ceded commissions and brokerage33,925 30,424 
As of
Consolidated balance sheetsMarch 31,
2026		December 31,
2025
Due from reinsurers$561,264 $537,366 
Due to reinsurers101,091 118,788 
v3.26.1
Per Share Data (Narrative) (Details) - shares
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Earnings Per Share [Abstract]    
Weighted average number of shares held in grantor trust (in shares) 17,378,810,000 17,659,297
v3.26.1
Per Share Data (Weighted Average Number of Common Shares Used In the Computation of Basic and Diluted Earnings per Share) (Details) - shares
shares in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Earnings Per Share [Abstract]    
Basic (shares) 392,264 396,929
Diluted (shares) 394,779 399,825
v3.26.1
Consolidated Statements of Comprehensive Income (Loss) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Beginning of period $ 9,711,894  
Other comprehensive (loss) income (150,180) $ 172,203
End of period 9,750,616  
Net realized and unrealized (losses) gains on investments (15,629) 15,711
Income before income taxes 616,098 538,606
Tax effect (100,523) (121,257)
Net income before noncontrolling interests 515,575 417,349
Total change in unrealized investment (losses) gains (185,971) 185,855
Net change in period (5,224) 23,930
Other comprehensive income (loss), pre-tax (191,195) 209,785
Other comprehensive income (loss), tax effect 41,015 (37,582)
Accumulated Other Comprehensive Income (Loss)    
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Beginning of period (451,097) (934,269)
Other comprehensive loss before reclassifications (153,634) 168,032
Amounts reclassified from AOCI 3,454 4,171
Other comprehensive (loss) income (150,180) 172,203
Unrealized investment loss related to noncontrolling interest 0 (1)
End of period (601,277) (762,067)
Accumulated Other Comprehensive Income (Loss) | Amounts reclassified from AOCI    
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Income before income taxes 4,372 5,280
Tax effect (918) (1,109)
Net income before noncontrolling interests 3,454 4,171
Unrealized investment losses:    
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Beginning of period (124,680) (517,170)
Other comprehensive loss before reclassifications (148,410) 144,102
Amounts reclassified from AOCI 3,454 4,171
Other comprehensive (loss) income (144,956) 148,273
Unrealized investment loss related to noncontrolling interest 0 (1)
End of period (269,636) (368,898)
Total change in unrealized investment (losses) gains (185,971) 185,855
Unrealized investment gains, tax effect 41,015 (37,582)
Unrealized investment gains (losses), after-tax amounts (144,956) 148,273
Unrealized investment losses: | Amounts reclassified from AOCI    
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Net realized and unrealized (losses) gains on investments 4,372 5,280
Tax effect (918) (1,109)
Net income before noncontrolling interests 3,454 4,171
Currency Translation Adjustments    
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Beginning of period (326,417) (417,099)
Other comprehensive loss before reclassifications (5,224) 23,930
Amounts reclassified from AOCI 0 0
Other comprehensive (loss) income (5,224) 23,930
Unrealized investment loss related to noncontrolling interest 0 0
End of period (331,641) (393,169)
Currency translation adjustment, pre-tax (5,224) 23,930
Currency translation adjustment, tax effect 0 0
Net change in period (5,224) 23,930
Currency Translation Adjustments | Amounts reclassified from AOCI    
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]    
Income before income taxes 0 0
Tax effect 0 0
Net income before noncontrolling interests $ 0 $ 0
v3.26.1
Statement of Cash Flows (Details) - USD ($)
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Cash and Cash Equivalents [Abstract]    
Interest payments $ 41,245,000 $ 41,193,000
Income tax refunds received $ 614,000 $ 18,740,000
v3.26.1
Investments in Fixed Maturity Securities (Investments in fixed maturity securities) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]        
Total held to maturity, Amortized Cost $ 30,925 $ 30,615    
Held-to-maturity, Allowance for Credit Loss 0 (9) $ (20) $ (25)
Held to maturity, Gross Unrealized Gains 609 872    
Held to maturity, Gross Unrealized Losses 0 0    
Total held to maturity, Fair Value 31,534 31,478    
Carrying Value 30,925 30,606    
Total available for sale, Amortized Cost 25,783,902 25,139,753    
Available-for-sale, Allowance for Credit Loss (306) (65) (333) (646)
Total available for sale, Gross Unrealized Gains 206,776 321,700    
Total available for sale, Gross Unrealized Losses (512,888) (444,332)    
Total available for sale, Fair Value 25,477,484 25,017,056    
Total fixed maturity securities available for sale 25,477,484 25,017,056    
Fixed maturity securities, amortized cost 25,814,827 25,170,368    
Fixed maturity securities, allowance for credit loss (306) (74)    
Total investments in fixed maturity securities, Gross Unrealized Gains 207,385 322,572    
Total investments in fixed maturity securities, Gross Unrealized Losses (512,888) (444,332)    
Total investments in fixed maturity securities, Fair Value 25,509,018 25,048,534    
Total investments in fixed maturity securities, Carrying Value 25,508,409 25,047,662    
State and municipal        
Debt Securities, Available-for-sale [Line Items]        
Total held to maturity, Amortized Cost 29,182 28,777    
Held-to-maturity, Allowance for Credit Loss 0 (9)    
Held to maturity, Gross Unrealized Gains 552 796    
Held to maturity, Gross Unrealized Losses 0 0    
Total held to maturity, Fair Value 29,734 29,564    
Carrying Value 29,182 28,768    
Total available for sale, Amortized Cost 1,778,905 1,862,104    
Available-for-sale, Allowance for Credit Loss 0 0 (10) 0
Total available for sale, Gross Unrealized Gains 10,490 13,503    
Total available for sale, Gross Unrealized Losses (37,588) (38,413)    
Total available for sale, Fair Value 1,751,807 1,837,194    
Total fixed maturity securities available for sale 1,751,807 1,837,194    
Residential mortgage-backed        
Debt Securities, Available-for-sale [Line Items]        
Total held to maturity, Amortized Cost 1,743 1,838    
Held-to-maturity, Allowance for Credit Loss 0 0    
Held to maturity, Gross Unrealized Gains 57 76    
Held to maturity, Gross Unrealized Losses 0 0    
Total held to maturity, Fair Value 1,800 1,914    
Carrying Value 1,743 1,838    
Total available for sale, Amortized Cost 4,592,286 4,584,970    
Available-for-sale, Allowance for Credit Loss (77) (65)    
Total available for sale, Gross Unrealized Gains 44,169 71,048    
Total available for sale, Gross Unrealized Losses (138,303) (132,645)    
Total available for sale, Fair Value 4,498,075 4,523,308    
Total fixed maturity securities available for sale 4,498,075 4,523,308    
U.S. government and government agency        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 4,378,606 3,964,375    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 37,479 48,820    
Total available for sale, Gross Unrealized Losses (32,512) (15,157)    
Total available for sale, Fair Value 4,383,573 3,998,038    
Total fixed maturity securities available for sale 4,383,573 3,998,038    
Special revenue        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 1,130,177 1,206,387    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 5,252 6,002    
Total available for sale, Gross Unrealized Losses (27,159) (27,943)    
Total available for sale, Fair Value 1,108,270 1,184,446    
Total fixed maturity securities available for sale 1,108,270 1,184,446    
State general obligation        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 201,814 203,543    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 2,287 3,465    
Total available for sale, Gross Unrealized Losses (3,804) (3,848)    
Total available for sale, Fair Value 200,297 203,160    
Total fixed maturity securities available for sale 200,297 203,160    
Pre-refunded        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 73,923 74,276    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 721 619    
Total available for sale, Gross Unrealized Losses (32) (111)    
Total available for sale, Fair Value 74,612 74,784    
Total fixed maturity securities available for sale 74,612 74,784    
Corporate backed        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 159,306 159,876    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 1,261 1,958    
Total available for sale, Gross Unrealized Losses (3,374) (3,459)    
Total available for sale, Fair Value 157,193 158,375    
Total fixed maturity securities available for sale 157,193 158,375    
Local general obligation        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 213,685 218,022    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 969 1,459    
Total available for sale, Gross Unrealized Losses (3,219) (3,052)    
Total available for sale, Fair Value 211,435 216,429    
Total fixed maturity securities available for sale 211,435 216,429    
Commercial        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 218,847 281,573    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 3,172 3,632    
Total available for sale, Gross Unrealized Losses (36) (35)    
Total available for sale, Fair Value 221,983 285,170    
Total fixed maturity securities available for sale 221,983 285,170    
Mortgage-backed        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 4,811,133 4,866,543    
Available-for-sale, Allowance for Credit Loss (77) (65) 0 (430)
Total available for sale, Gross Unrealized Gains 47,341 74,680    
Total available for sale, Gross Unrealized Losses (138,339) (132,680)    
Total available for sale, Fair Value 4,720,058 4,808,478    
Total fixed maturity securities available for sale 4,720,058 4,808,478    
Asset-backed        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 3,881,752 3,807,393    
Available-for-sale, Allowance for Credit Loss (229) 0 0 0
Total available for sale, Gross Unrealized Gains 10,025 20,196    
Total available for sale, Gross Unrealized Losses (22,603) (17,243)    
Total available for sale, Fair Value 3,868,945 3,810,346    
Total fixed maturity securities available for sale 3,868,945 3,810,346    
Industrial        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 3,514,642 3,627,567    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 36,565 57,466    
Total available for sale, Gross Unrealized Losses (39,478) (36,499)    
Total available for sale, Fair Value 3,511,729 3,648,534    
Total fixed maturity securities available for sale 3,511,729 3,648,534    
Financial        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 3,526,804 3,438,348    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 34,606 61,180    
Total available for sale, Gross Unrealized Losses (26,851) (16,460)    
Total available for sale, Fair Value 3,534,559 3,483,068    
Total fixed maturity securities available for sale 3,534,559 3,483,068    
Utilities        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 1,521,021 1,300,506    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 12,721 22,593    
Total available for sale, Gross Unrealized Losses (14,083) (8,878)    
Total available for sale, Fair Value 1,519,659 1,314,221    
Total fixed maturity securities available for sale 1,519,659 1,314,221    
Other        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 209,346 240,374    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 1,365 2,356    
Total available for sale, Gross Unrealized Losses (488) (1,142)    
Total available for sale, Fair Value 210,223 241,588    
Total fixed maturity securities available for sale 210,223 241,588    
Corporate        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 8,771,813 8,606,795    
Available-for-sale, Allowance for Credit Loss 0 0    
Total available for sale, Gross Unrealized Gains 85,257 143,595    
Total available for sale, Gross Unrealized Losses (80,900) (62,979)    
Total available for sale, Fair Value 8,776,170 8,687,411    
Total fixed maturity securities available for sale 8,776,170 8,687,411    
Foreign government        
Debt Securities, Available-for-sale [Line Items]        
Total available for sale, Amortized Cost 2,161,693 2,032,543    
Available-for-sale, Allowance for Credit Loss 0 0 $ (323) $ (216)
Total available for sale, Gross Unrealized Gains 16,184 20,906    
Total available for sale, Gross Unrealized Losses (200,946) (177,860)    
Total available for sale, Fair Value 1,976,931 1,875,589    
Total fixed maturity securities available for sale $ 1,976,931 $ 1,875,589    
v3.26.1
Investments in Fixed Maturity Securities (HTM Allowance for Credit Loss) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period $ 9 $ 25
Cumulative effect adjustment resulting from changes in accounting principles 0 20
Provision for expected credit losses (9) (5)
Balance, end of period $ 0 $ 20
v3.26.1
Investments in Fixed Maturity Securities (AFS Allowance for Credit Loss) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period $ 65 $ 646
Change on securities for which credit losses were not previously recorded 229 10
Change on securities for which credit losses were previously recorded 12 (323)
Balance, end of period 306 333
Foreign government    
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period 0 216
Change on securities for which credit losses were not previously recorded 0 0
Change on securities for which credit losses were previously recorded 0 107
Balance, end of period 0 323
Mortgage-backed    
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period 65 430
Change on securities for which credit losses were not previously recorded 0 0
Change on securities for which credit losses were previously recorded 12 (430)
Balance, end of period 77 0
State and municipal    
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period 0 0
Change on securities for which credit losses were not previously recorded 0 10
Change on securities for which credit losses were previously recorded 0 0
Balance, end of period 0 10
Corporate    
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period 0  
Balance, end of period 0  
Asset-backed    
Debt Securities, Available-for-sale, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period 0 0
Change on securities for which credit losses were not previously recorded 229 0
Change on securities for which credit losses were previously recorded 0 0
Balance, end of period $ 229 $ 0
v3.26.1
Investments in Fixed Maturity Securities (Amortized cost and fair value of fixed maturity securities) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract]        
Amortized Cost, Due in one year or less $ 1,859,542      
Amortized Cost, Due after one year through five years 7,947,108      
Amortized Cost, Due after five years through ten years 3,963,797      
Amortized Cost, Due after ten years 7,231,504      
Amortized Cost, Mortgaged-backed securities 4,812,876      
Total investments in fixed maturity securities, Amortized Value 25,814,827      
Fair Value, Due in one year or less 1,811,447      
Fair Value, Due after one year through five years 7,814,089      
Fair Value, Due after five years through ten years 3,959,533      
Fair Value, Due after ten years 7,202,091      
Fair Value, Mortgage-backed securities 4,721,858      
Total investments in fixed maturity securities, Fair Value 25,509,018 $ 25,048,534    
Cumulative effect adjustment resulting from changes in accounting principles $ 0 $ 9 $ 20 $ 25
v3.26.1
Investments in Equity Securities (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2026
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]    
Equity securities $ 1,469,651 $ 1,358,201
Fair Value    
Debt Securities, Available-for-sale [Line Items]    
Cost 1,115,993 1,000,049
Gross Unrealized, Gains 368,148 369,011
Gross Unrealized, Losses (14,490) (10,859)
Equity securities 1,469,651 1,358,201
Fair Value | Common stock    
Debt Securities, Available-for-sale [Line Items]    
Cost 602,744 566,577
Gross Unrealized, Gains 255,501 181,120
Gross Unrealized, Losses (8,575) (5,584)
Equity securities 849,670 742,113
Fair Value | Preferred stocks    
Debt Securities, Available-for-sale [Line Items]    
Cost 513,249 433,472
Gross Unrealized, Gains 112,647 187,891
Gross Unrealized, Losses (5,915) (5,275)
Equity securities 619,981 616,088
Carrying Value    
Debt Securities, Available-for-sale [Line Items]    
Equity securities 1,469,651 1,358,201
Carrying Value | Common stock    
Debt Securities, Available-for-sale [Line Items]    
Equity securities 849,670 742,113
Carrying Value | Preferred stocks    
Debt Securities, Available-for-sale [Line Items]    
Equity securities $ 619,981 $ 616,088
v3.26.1
Arbitrage Trading Account (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Derivative [Line Items]    
Arbitrage trading account $ 1,165,000 $ 1,221,000
Short | Options held    
Derivative [Line Items]    
Fair value of derivative 33  
Notional amount of derivative $ 1,000  
v3.26.1
Net Investment Income (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Net Investment Income [Line Items]    
Gross investment income $ 407,255 $ 363,764
Investment expense (2,922) (3,472)
Net investment income 404,333 360,292
Fixed maturity securities, including cash and cash equivalents and loans receivable    
Net Investment Income [Line Items]    
Gross investment income 346,527 313,788
Arbitrage Trading Account    
Net Investment Income [Line Items]    
Gross investment income 10,313 16,329
Equity Securities    
Net Investment Income [Line Items]    
Gross investment income 15,819 10,641
Arbitrage trading account (1)    
Net Investment Income [Line Items]    
Gross investment income 39,529 27,023
Real estate    
Net Investment Income [Line Items]    
Gross investment income $ (4,933) $ (4,017)
v3.26.1
Investment Funds (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Schedule of Equity Method Investments [Line Items]      
Unfunded commitments $ 251,000    
Investment funds 1,398,022   $ 1,361,802
Income (Loss) from Investment Funds 39,529 $ 27,023  
Written premiums ceded 611,421 550,637  
Fair Value      
Schedule of Equity Method Investments [Line Items]      
Trading account receivables from brokers and clearing organizations 8,690   11,669
Financial services (1)      
Schedule of Equity Method Investments [Line Items]      
Investment funds 157,089   163,098
Income (Loss) from Investment Funds 8,016 4,965  
Transportation      
Schedule of Equity Method Investments [Line Items]      
Investment funds 365,731   360,320
Income (Loss) from Investment Funds 7,402 7,114  
Real Estate      
Schedule of Equity Method Investments [Line Items]      
Investment funds 275,546   272,775
Income (Loss) from Investment Funds 8,660 8,615  
Energy      
Schedule of Equity Method Investments [Line Items]      
Investment funds 43,565   41,966
Income (Loss) from Investment Funds 2,433 (2,102)  
Infrastructure      
Schedule of Equity Method Investments [Line Items]      
Investment funds 176,316   169,847
Income (Loss) from Investment Funds 5,792 3,502  
Other funds      
Schedule of Equity Method Investments [Line Items]      
Investment funds 379,775   353,796
Income (Loss) from Investment Funds 7,226 $ 4,929  
Deferred compensation trust assets $ 47,000   $ 43,000
v3.26.1
Real Estate (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Real Estate [Abstract]    
Properties in operation $ 1,075,345 $ 1,051,455
Properties under development 228,396 228,293
Total $ 1,303,741 $ 1,279,748
v3.26.1
Real Estate (Narrative) (Details) - USD ($)
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Real Estate [Abstract]      
Accumulated depreciation and amortization on properties $ 44,088,000   $ 41,942,000
Real estate depreciation expense 2,570,000 $ 2,228,000  
Lease future minimum payments 2021 28,469,051    
Lease future minimum payments 2022 41,187,585    
Lease future minimum payments 2023 44,955,741    
Lease future minimum payments 2024 40,347,609    
Lease future minimum payments 2025 34,499,456    
Lease future minimum payments 2026 29,851,700    
Lease future minimum payments there after $ 362,556,463    
v3.26.1
Loans Receivable (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans receivable, gross $ 441,160 $ 418,913
Real estate loans    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Loans receivable, gross 441,160 418,913
Loans receivable $ 441,236 $ 419,074
v3.26.1
Loans Receivable - Allowance For Credit Loss (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Financing Receivable, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period $ 161 $ 1,114
Change in expected credit losses (86) (326)
Balance, end of period 75 788
Real estate loans    
Financing Receivable, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period 161 1,088
Change in expected credit losses (86) (312)
Balance, end of period 75 776
Commercial loans    
Financing Receivable, Allowance for Credit Loss [Roll Forward]    
Balance, beginning of period 0 26
Change in expected credit losses 0 (14)
Balance, end of period $ 0 $ 12
v3.26.1
Net Investment (Losses) Gains (Net Investment Gains (Losses)) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Investments, Debt and Equity Securities [Abstract]    
Fixed maturity securities, gains $ 5,148 $ 2,632
Fixed maturity securities, losses (6,537) (2,712)
Net realized gains (losses) on investment sales 1 (2,595)
Change in unrealized (losses) gains (4,494) 19,947
Investment funds 173 14
Real estate (7,298) 3,943
Loans receivable 131 0
Other (2,753) (5,518)
Net realized and unrealized (losses) gains on investments in earnings before allowance for expected credit losses (15,629) 15,711
Fixed maturity securities (232) 318
Loans receivable 86 326
Change in allowance for expected credit losses on investments (146) 644
Net investment (losses) gains (15,775) 16,355
Income tax benefit (expense) 3,381 (3,528)
After-tax net investment (losses) gains $ (12,394) $ 12,827
v3.26.1
Net Investment (Losses) Gains (Change in Unrealized Gains (Losses) of Available For Sales Securities) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Realized and Unrealized Investment Gains Losses [Line Items]    
Total change in unrealized investment (losses) gains $ (185,971) $ 185,855
Income tax benefit (expense) 41,015 (37,582)
Noncontrolling interests 0 (1)
Total change in unrealized gains (144,956) 148,272
Debt securities    
Realized and Unrealized Investment Gains Losses [Line Items]    
Total change in unrealized investment (losses) gains (183,478) 183,987
Fixed maturity securities with allowance for expected credit losses    
Realized and Unrealized Investment Gains Losses [Line Items]    
Total change in unrealized investment (losses) gains (2) (551)
Investment funds    
Realized and Unrealized Investment Gains Losses [Line Items]    
Total change in unrealized investment (losses) gains (2,519) 2,496
Other    
Realized and Unrealized Investment Gains Losses [Line Items]    
Total change in unrealized investment (losses) gains $ 28 $ (77)
v3.26.1
Fixed Maturity Securities In An Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]    
Fair Value, Less than 12 Months $ 7,420,057 $ 2,988,258
Gross Unrealized Losses, Less than 12 Months 91,736 28,408
Fair Value, 12 Months or Greater 4,046,489 4,652,566
Gross Unrealized Losses, 12 Months or Greater 421,152 415,924
Fair Value, Total 11,466,546 7,640,824
Gross Unrealized Losses, Total 512,888 444,332
U.S. government and government agency    
Debt Securities, Available-for-sale [Line Items]    
Fair Value, Less than 12 Months 1,605,859 790,077
Gross Unrealized Losses, Less than 12 Months 27,355 8,902
Fair Value, 12 Months or Greater 134,391 183,896
Gross Unrealized Losses, 12 Months or Greater 5,157 6,255
Fair Value, Total 1,740,250 973,973
Gross Unrealized Losses, Total 32,512 15,157
State and municipal    
Debt Securities, Available-for-sale [Line Items]    
Fair Value, Less than 12 Months 272,890 141,680
Gross Unrealized Losses, Less than 12 Months 2,390 1,520
Fair Value, 12 Months or Greater 919,184 1,053,168
Gross Unrealized Losses, 12 Months or Greater 35,198 36,893
Fair Value, Total 1,192,074 1,194,848
Gross Unrealized Losses, Total 37,588 38,413
Mortgage-backed    
Debt Securities, Available-for-sale [Line Items]    
Fair Value, Less than 12 Months 960,232 251,861
Gross Unrealized Losses, Less than 12 Months 11,297 2,265
Fair Value, 12 Months or Greater 683,839 839,061
Gross Unrealized Losses, 12 Months or Greater 127,042 130,415
Fair Value, Total 1,644,071 1,090,922
Gross Unrealized Losses, Total 138,339 132,680
Asset-backed    
Debt Securities, Available-for-sale [Line Items]    
Fair Value, Less than 12 Months 1,565,320 644,346
Gross Unrealized Losses, Less than 12 Months 6,184 1,643
Fair Value, 12 Months or Greater 518,177 503,876
Gross Unrealized Losses, 12 Months or Greater 16,419 15,600
Fair Value, Total 2,083,497 1,148,222
Gross Unrealized Losses, Total 22,603 17,243
Corporate    
Debt Securities, Available-for-sale [Line Items]    
Fair Value, Less than 12 Months 1,963,231 494,240
Gross Unrealized Losses, Less than 12 Months 24,464 4,308
Fair Value, 12 Months or Greater 1,538,307 1,786,925
Gross Unrealized Losses, 12 Months or Greater 56,436 58,671
Fair Value, Total 3,501,538 2,281,165
Gross Unrealized Losses, Total 80,900 62,979
Foreign government    
Debt Securities, Available-for-sale [Line Items]    
Fair Value, Less than 12 Months 1,052,525 666,054
Gross Unrealized Losses, Less than 12 Months 20,046 9,770
Fair Value, 12 Months or Greater 252,591 285,640
Gross Unrealized Losses, 12 Months or Greater 180,900 168,090
Fair Value, Total 1,305,116 951,694
Gross Unrealized Losses, Total $ 200,946 $ 177,860
v3.26.1
Fixed Maturity Securities In An Unrealized Loss Position (Non-Investment Grade Fixed Maturity Securities) (Details) - External Credit Rating, Noninvestment Grade
$ in Thousands
Mar. 31, 2026
USD ($)
Debt Securities, Available-for-sale [Line Items]  
Number of Securities 93
Aggregate Fair Value $ 212,844
Gross Unrealized Loss $ 176,687
Foreign government  
Debt Securities, Available-for-sale [Line Items]  
Number of Securities 59
Aggregate Fair Value $ 159,082
Gross Unrealized Loss $ 174,727
Corporate  
Debt Securities, Available-for-sale [Line Items]  
Number of Securities 15
Aggregate Fair Value $ 22,759
Gross Unrealized Loss $ 950
State and municipal  
Debt Securities, Available-for-sale [Line Items]  
Number of Securities 5
Aggregate Fair Value $ 29,106
Gross Unrealized Loss $ 894
Mortgage-backed  
Debt Securities, Available-for-sale [Line Items]  
Number of Securities 14
Aggregate Fair Value $ 1,897
Gross Unrealized Loss $ 116
v3.26.1
Fair Value Measurements (Assets and Liabilities Measured At Fair Value, On a Recurring Basis) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Assets:    
Total fixed maturity securities available for sale $ 25,477,484 $ 25,017,056
Equity securities 1,469,651 1,358,201
Arbitrage trading account 1,165,000 1,221,000
Fair Value, Measurements, Recurring    
Assets:    
Total fixed maturity securities available for sale 25,477,484 25,017,056
Equity securities 1,469,651 1,358,201
Arbitrage trading account 1,164,872 1,221,103
Total 28,112,007 27,596,360
Liabilities:    
Trading account securities sold but not yet purchased 33 66,285
Fair Value, Measurements, Recurring | U.S. government and government agency    
Assets:    
Total fixed maturity securities available for sale 4,383,573 3,998,038
Fair Value, Measurements, Recurring | State and municipal    
Assets:    
Total fixed maturity securities available for sale 1,751,807 1,837,194
Fair Value, Measurements, Recurring | Mortgage-backed    
Assets:    
Total fixed maturity securities available for sale 4,720,058 4,808,478
Fair Value, Measurements, Recurring | Asset-backed    
Assets:    
Total fixed maturity securities available for sale 3,868,945 3,810,346
Fair Value, Measurements, Recurring | Corporate    
Assets:    
Total fixed maturity securities available for sale 8,776,170 8,687,411
Fair Value, Measurements, Recurring | Foreign government    
Assets:    
Total fixed maturity securities available for sale 1,976,931 1,875,589
Fair Value, Measurements, Recurring | Common stocks    
Assets:    
Equity securities 849,670 742,113
Fair Value, Measurements, Recurring | Preferred stocks    
Assets:    
Equity securities 619,981 616,088
Level 1 | Fair Value, Measurements, Recurring    
Assets:    
Total fixed maturity securities available for sale 0 0
Equity securities 846,795 739,186
Arbitrage trading account 1,058,448 1,139,447
Total 1,905,243 1,878,633
Liabilities:    
Trading account securities sold but not yet purchased 33 66,285
Level 1 | Fair Value, Measurements, Recurring | U.S. government and government agency    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 1 | Fair Value, Measurements, Recurring | State and municipal    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 1 | Fair Value, Measurements, Recurring | Mortgage-backed    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 1 | Fair Value, Measurements, Recurring | Asset-backed    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 1 | Fair Value, Measurements, Recurring | Corporate    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 1 | Fair Value, Measurements, Recurring | Foreign government    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 1 | Fair Value, Measurements, Recurring | Common stocks    
Assets:    
Equity securities 846,795 739,186
Level 1 | Fair Value, Measurements, Recurring | Preferred stocks    
Assets:    
Equity securities 0 0
Level 2 | Fair Value, Measurements, Recurring    
Assets:    
Total fixed maturity securities available for sale 25,457,613 24,997,055
Equity securities 612,079 608,200
Arbitrage trading account 106,311 81,543
Total 26,176,003 25,686,798
Liabilities:    
Trading account securities sold but not yet purchased 0 0
Level 2 | Fair Value, Measurements, Recurring | U.S. government and government agency    
Assets:    
Total fixed maturity securities available for sale 4,383,573 3,998,038
Level 2 | Fair Value, Measurements, Recurring | State and municipal    
Assets:    
Total fixed maturity securities available for sale 1,751,807 1,837,194
Level 2 | Fair Value, Measurements, Recurring | Mortgage-backed    
Assets:    
Total fixed maturity securities available for sale 4,720,058 4,808,478
Level 2 | Fair Value, Measurements, Recurring | Asset-backed    
Assets:    
Total fixed maturity securities available for sale 3,868,945 3,810,346
Level 2 | Fair Value, Measurements, Recurring | Corporate    
Assets:    
Total fixed maturity securities available for sale 8,756,299 8,667,410
Level 2 | Fair Value, Measurements, Recurring | Foreign government    
Assets:    
Total fixed maturity securities available for sale 1,976,931 1,875,589
Level 2 | Fair Value, Measurements, Recurring | Common stocks    
Assets:    
Equity securities 772 786
Level 2 | Fair Value, Measurements, Recurring | Preferred stocks    
Assets:    
Equity securities 611,307 607,414
Level 3 | Fair Value, Measurements, Recurring    
Assets:    
Total fixed maturity securities available for sale 19,871 20,001
Equity securities 10,777 10,815
Arbitrage trading account 113 113
Total 30,761 30,929
Liabilities:    
Trading account securities sold but not yet purchased 0 0
Level 3 | Fair Value, Measurements, Recurring | U.S. government and government agency    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 3 | Fair Value, Measurements, Recurring | State and municipal    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 3 | Fair Value, Measurements, Recurring | Mortgage-backed    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 3 | Fair Value, Measurements, Recurring | Asset-backed    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 3 | Fair Value, Measurements, Recurring | Corporate    
Assets:    
Total fixed maturity securities available for sale 19,871 20,001
Level 3 | Fair Value, Measurements, Recurring | Foreign government    
Assets:    
Total fixed maturity securities available for sale 0 0
Level 3 | Fair Value, Measurements, Recurring | Common stocks    
Assets:    
Equity securities 2,103 2,141
Level 3 | Fair Value, Measurements, Recurring | Preferred stocks    
Assets:    
Equity securities $ 8,674 $ 8,674
v3.26.1
Fair Value Measurements (Summarize Changes in Level 3 Assets) (Details) - Level 3 - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2026
Dec. 31, 2025
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Assets, beginning balance $ 30,929 $ 28,892
Assets, earnings (38) 1,971
Assets, other comprehensive income (130) 334
Assets, purchases 0 6,160
Assets, (sales) 0 (6,429)
Assets. transfers out   1
Securities transferred into or out of level 3, net 0  
Assets, ending balance 30,761 30,929
Debt securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Assets, beginning balance 20,001 19,667
Assets, earnings 0 0
Assets, other comprehensive income (130) 334
Assets, purchases 0 0
Assets, (sales) 0 0
Assets. transfers out   0
Securities transferred into or out of level 3, net 0  
Assets, ending balance 19,871 20,001
Equity Securities    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Assets, beginning balance 10,815 5,715
Assets, earnings (38) 226
Assets, other comprehensive income 0 0
Assets, purchases 0 6,160
Assets, (sales) 0 (1,286)
Assets. transfers out 0 0
Assets, ending balance 10,777 10,815
Common stock    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Assets, beginning balance 2,141 2,041
Assets, earnings (38) 226
Assets, other comprehensive income 0 0
Assets, purchases 0 0
Assets, (sales) 0 (126)
Assets. transfers out 0 0
Assets, ending balance 2,103 2,141
Preferred stocks    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Assets, beginning balance 8,674 3,674
Assets, earnings 0 0
Assets, other comprehensive income 0 0
Assets, purchases 0 6,160
Assets, (sales) 0 (1,160)
Assets. transfers out 0 0
Assets, ending balance 8,674 8,674
Arbitrage trading account    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Assets, beginning balance 113 3,510
Assets, earnings 0 1,745
Assets, other comprehensive income 0 0
Assets, purchases 0 0
Assets, (sales) 0 (5,143)
Assets. transfers out   1
Securities transferred into or out of level 3, net 0  
Assets, ending balance 113 113
Corporate    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Assets, beginning balance 20,001 19,667
Assets, earnings 0 0
Assets, other comprehensive income (130) 334
Assets, purchases 0 0
Assets, (sales) 0 0
Securities transferred into or out of level 3, net 0 0
Assets, ending balance $ 19,871 $ 20,001
v3.26.1
Reserves for Loss and Loss Expenses (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]      
Net reserves at beginning of period $ 18,953,674 $ 17,166,641  
Net provision for losses and loss expenses:      
Claims occurring during the current year 1,922,419 1,883,708  
Decrease in estimates for claims occurring in prior years 5,435 9,604  
Loss reserve discount accretion 8,171 7,480  
Total 1,936,025 1,900,792  
Net payments for claims:      
Current year 118,765 127,193  
Prior years 1,424,066 1,304,763  
Total 1,542,831 1,431,956  
Foreign currency translation 777 43,780  
Net reserves at end of period 19,347,645 17,679,257 $ 18,953,674
Ceded reserves at end of period 3,268,615 3,242,730  
Gross reserves at end of period $ 22,616,260 $ 20,921,987 $ 22,207,773
v3.26.1
Reserves for Loss and Loss Expenses (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Liability for Claims and Claims Adjustment Expense [Line Items]    
Net of loss reserves discount $ 17 $ 14
Increase in estimates for claims 2 12
Adjustment expense 1 1
Insurance    
Liability for Claims and Claims Adjustment Expense [Line Items]    
Unfavorable reserve development net of premium offsets 8 11
Reinsurance & Monoline Excess    
Liability for Claims and Claims Adjustment Expense [Line Items]    
Favorable reserve development net of premium offsets $ 9 $ 12
v3.26.1
Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Assets:    
Equity securities $ 1,469,651 $ 1,358,201
Arbitrage trading account 1,165,000 1,221,000
Carrying Value    
Assets:    
Fixed maturity securities 25,508,409 25,047,662
Equity securities 1,469,651 1,358,201
Arbitrage trading account 1,164,872 1,221,103
Loans receivable 441,160 418,913
Cash and cash equivalents 2,280,934 2,539,938
Trading account receivables from brokers and clearing organizations 8,690 11,669
Due from broker 0 629
Liabilities:    
Due to broker 157,034 0
Trading account securities sold but not yet purchased 33 66,285
Senior notes and other debt 1,830,328 1,829,198
Subordinated debentures 1,010,707 1,010,527
Fair Value    
Assets:    
Fixed maturity securities 25,509,018 25,048,534
Equity securities 1,469,651 1,358,201
Arbitrage trading account 1,164,872 1,221,103
Loans receivable 441,236 419,074
Cash and cash equivalents 2,280,934 2,539,938
Trading account receivables from brokers and clearing organizations 8,690 11,669
Due from broker 0 629
Liabilities:    
Due to broker 157,034 0
Trading account securities sold but not yet purchased 33 66,285
Senior notes and other debt 1,417,275 1,440,055
Subordinated debentures $ 730,234 $ 760,400
v3.26.1
Premiums and Reinsurance Related Information (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Written premiums:    
Written premiums, direct $ 3,471,186 $ 3,310,893
Written premiums, assumed 314,580 373,046
Written premiums, ceded (611,421) (550,637)
Total net premiums written 3,174,345 3,133,302
Earned premiums:    
Earned premiums, direct 3,424,142 3,233,843
Earned premiums, assumed 314,934 339,596
Earned premiums, ceded (623,904) (561,058)
Earned premiums 3,115,172 3,012,381
Ceded losses and loss expenses incurred 357,740 314,252
Ceded commissions earned $ 152,948 $ 139,604
v3.26.1
Premiums and Reinsurance Related Information - Premiums and Reinsurance, Allowance For Credit Loss (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Premium Receivable, Allowance for Credit Loss [Roll Forward]    
Allowance for expected credit losses, beginning of period $ 42,006 $ 39,884
Cumulative effect adjustment resulting from changes in accounting principles 42,130 38,861
Change in expected credit losses 124 (1,023)
Allowance for expected credit losses, end of period 42,130 38,861
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]    
Allowance for expected credit losses, beginning of period 6,378 8,350
Cumulative effect adjustment resulting from changes in accounting principles 4,972 7,084
Reinsurance Recoverable, Credit Loss Expense (Reversal) (1,406) (1,266)
Allowance for expected credit losses, end of period $ 4,972 $ 7,084
v3.26.1
Restricted Stock Units (Summary of Restricted Stock Units Issued) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]    
Share based compensation expense $ 13,000 $ 12,000
Restricted stock    
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]    
Restricted stock units (in units) 6,045 20,647
Fair Value $ 432 $ 1,210
Minimum | Restricted stock    
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]    
Award vesting period 3 years  
Maximum | Restricted stock    
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]    
Award vesting period 5 years  
v3.26.1
Litigation and Contingent Liabilities (Details) - Subsidiary of Common Parent
Dec. 22, 2023
plantiff
Loss Contingencies [Line Items]  
Number of plantiff 1
Insurance Claims  
Loss Contingencies [Line Items]  
Estimated recovery in respect of certain losses paid policy holders 90 million
v3.26.1
Leases (Lease Cost) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Leases [Abstract]    
Lease cost $ 13,915 $ 12,778
Cash paid for amounts included in the measurement of lease liabilities reported in operating cash flows 12,097 13,482
Right-of-use assets obtained in exchange for new lease liabilities $ 3,760 $ 13,210
v3.26.1
Leases (Supplemental Balance Sheet Information) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Mar. 31, 2025
Leases [Abstract]    
Operating lease, right-of-use asset $ 215,547 $ 185,373
Operating lease, liability $ 255,715 $ 222,855
Weighted-average remaining lease term 7 years 7 years 2 months 12 days
Weighted-average discount rate 6.00% 5.67%
v3.26.1
Leases (Maturities of Operating Lease Liabilities) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Mar. 31, 2025
Leases [Abstract]    
2026 $ 40,758  
2027 48,450  
2028 46,802  
2029 42,731  
2030 37,907  
Thereafter 99,086  
Total undiscounted future minimum lease payments 315,734  
Less: Discount impact 60,019  
Total lease liability $ 255,715 $ 222,855
v3.26.1
Business Segments (Financial Information of Company Operating Segments) (Details)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
USD ($)
segment
Mar. 31, 2025
USD ($)
Segment Reporting [Abstract]    
Number of reportable segments | segment 2  
Number of operating segments | segment 3  
Segment Reporting Information [Line Items]    
Premiums Earned, Net $ 3,115,172 $ 3,012,381
Investment Income 404,333 360,292
Other 170,829 174,726
Total revenues 3,690,334 3,547,399
Net Income (Loss) to Common Stockholders 515,216 417,571
Net investment gains (15,775) 16,355
Net investment gains, net of tax (12,394) 12,827
Income before income taxes 616,098 538,606
Policyholder Benefits and Claims Incurred, Net 1,936,025 1,900,792
Policy Acquisition And Insurance Operating Expenses 889,185 838,246
Other segment amount 249,026 269,755
Total 3,074,236 3,008,793
Net investment (losses) gains (15,775) 16,355
Corporate Reconciling Items And Eliminations    
Segment Reporting Information [Line Items]    
Investment Income 25,243 2,614
Other 176,761 148,419
Total revenues 202,004 151,033
Net Income (Loss) to Common Stockholders (28,224) (84,221)
Income before income taxes (35,496) (107,634)
Other segment amount 237,500 258,667
Total 237,500 258,667
Segment Reporting, Reconciling Item, Corporate Nonsegment    
Segment Reporting Information [Line Items]    
Income before income taxes (15,775) 16,355
Net investment (losses) gains (15,775)  
Insurance    
Segment Reporting Information [Line Items]    
Premiums Earned, Net   2,642,507
Insurance | Operating Segments    
Segment Reporting Information [Line Items]    
Premiums Earned, Net 2,765,492 2,642,507
Investment Income 311,241 291,248
Other 9,843 9,952
Total revenues 3,086,576 2,943,707
Net Income (Loss) to Common Stockholders 433,467 393,122
Income before income taxes 524,663 509,505
Policyholder Benefits and Claims Incurred, Net 1,766,968 1,687,453
Policy Acquisition And Insurance Operating Expenses 783,419 735,661
Other segment amount 11,526 11,088
Total 2,561,913 2,434,202
Insurance | Operating Segments | Non-US    
Segment Reporting Information [Line Items]    
Total revenues 376,000 333,000
Reinsurance & Monoline Excess    
Segment Reporting Information [Line Items]    
Premiums Earned, Net   369,874
Reinsurance & Monoline Excess | Operating Segments    
Segment Reporting Information [Line Items]    
Premiums Earned, Net 349,680 369,874
Investment Income 67,849 66,430
Other 0 0
Total revenues 417,529 436,304
Net Income (Loss) to Common Stockholders 122,367 95,843
Income before income taxes 142,706 120,380
Policyholder Benefits and Claims Incurred, Net 169,057 213,339
Policy Acquisition And Insurance Operating Expenses 105,766 102,585
Total 274,823 315,924
Reinsurance & Monoline Excess | Operating Segments | Non-US    
Segment Reporting Information [Line Items]    
Total revenues $ 113,000 $ 130,000
v3.26.1
Business Segments (Identifiable Assets by Segment) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Segment Reporting, Asset Reconciling Item [Line Items]    
Consolidated Assets $ 44,315,553 $ 43,926,843
Operating Segments | Insurance    
Segment Reporting, Asset Reconciling Item [Line Items]    
Consolidated Assets 35,954,379 35,686,306
Operating Segments | Reinsurance & Monoline Excess    
Segment Reporting, Asset Reconciling Item [Line Items]    
Consolidated Assets 5,777,792 5,891,538
Corporate Reconciling Items And Eliminations    
Segment Reporting, Asset Reconciling Item [Line Items]    
Consolidated Assets $ 2,583,382 $ 2,348,999
v3.26.1
Business Segments (Net Premiums Earned By Major Line of Business) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Revenue from External Customer [Line Items]    
Earned premiums $ 3,115,172 $ 3,012,381
Insurance    
Revenue from External Customer [Line Items]    
Earned premiums   2,642,507
Insurance | Operating Segments    
Revenue from External Customer [Line Items]    
Earned premiums 2,765,492 2,642,507
Insurance | Other liability    
Revenue from External Customer [Line Items]    
Earned premiums 1,097,841 1,072,728
Insurance | Short-tail lines    
Revenue from External Customer [Line Items]    
Earned premiums 652,523 596,109
Insurance | Auto    
Revenue from External Customer [Line Items]    
Earned premiums 413,492 389,949
Insurance | Workers' compensation    
Revenue from External Customer [Line Items]    
Earned premiums 313,742 311,028
Insurance | Professional liability    
Revenue from External Customer [Line Items]    
Earned premiums 287,894 272,693
Reinsurance & Monoline Excess    
Revenue from External Customer [Line Items]    
Earned premiums   369,874
Reinsurance & Monoline Excess | Operating Segments    
Revenue from External Customer [Line Items]    
Earned premiums 349,680 369,874
Reinsurance & Monoline Excess | Casualty    
Revenue from External Customer [Line Items]    
Earned premiums 171,719 181,767
Reinsurance & Monoline Excess | Monoline excess    
Revenue from External Customer [Line Items]    
Earned premiums 76,109 67,264
Reinsurance & Monoline Excess | Property    
Revenue from External Customer [Line Items]    
Earned premiums $ 101,852 $ 120,843
v3.26.1
Related-Party Transactions - Narrative (Details) - USD ($)
$ in Thousands
 3 Months Ended
Jan. 01, 2025
Jul. 01, 2022
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Related Party Transaction [Line Items]          
Current capitalization     $ 9,739,550   $ 9,700,818
Ceded commissions earned     152,948 $ 139,604  
Written premiums, Ceded     611,421 550,637  
Due to reinsurers     627,760   615,781
Written premiums, assumed     $ 314,580 373,046  
Mitsui Sumitomo Insurance Co., Ltd. | Common stocks          
Related Party Transaction [Line Items]          
Percent of stock held by related party     15.80%    
Nonrelated Party | Lifson Re          
Related Party Transaction [Line Items]          
Current capitalization     $ 418,000    
Nonrelated Party | Lifson Re | Management And Performance Fees          
Related Party Transaction [Line Items]          
Ceded commissions earned     3,000 1,000  
Nonrelated Party | Reinsurer Concentration Risk | Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Lifson Re          
Related Party Transaction [Line Items]          
Concentration risk, percentage 32.50% 30.00%      
Written premiums, Ceded     118,517 106,137  
Ceded commissions and brokerage     33,925 $ 30,424  
Due from reinsurers     561,264   537,366
Due to reinsurers     101,091   $ 118,788
Nonrelated Party | Reinsurer Concentration Risk | Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Mitsui Sumitomo Insurance Co., Ltd.          
Related Party Transaction [Line Items]          
Written premiums, Ceded     15,000    
Ceded commissions and brokerage     3,000    
Due from reinsurers     61,000    
Due to reinsurers     11,000    
Written premiums, assumed     5,000    
Assumed premiums receivable     5,000    
Assumed premiums payable     $ 11,000    
v3.26.1
Related-Party Transactions - Schedule (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Related Party Transaction [Line Items]      
Written premiums ceded $ 611,421 $ 550,637  
Due to reinsurers 627,760   $ 615,781
Nonrelated Party | Lifson Re | Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Reinsurer Concentration Risk      
Related Party Transaction [Line Items]      
Written premiums ceded 118,517 106,137  
Ceded commissions and brokerage 33,925 $ 30,424  
Due from reinsurers 561,264   537,366
Due to reinsurers 101,091   $ 118,788
Nonrelated Party | Mitsui Sumitomo Insurance Co., Ltd. | Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments | Reinsurer Concentration Risk      
Related Party Transaction [Line Items]      
Written premiums ceded 15,000    
Ceded commissions and brokerage 3,000    
Due from reinsurers 61,000    
Due to reinsurers $ 11,000