COMPASS MINERALS INTERNATIONAL INC, 10-Q filed on 5/7/2026
Quarterly Report
v3.26.1
Cover Page - shares
 6 Months Ended
Mar. 31, 2026
Apr. 30, 2026
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2026  
Document Transition Report false  
Entity File Number 001-31921  
Entity Registrant Name Compass Minerals International, Inc.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 36-3972986  
Entity Address, Address Line One 9900 West 109th Street  
Entity Address, Address Line Two Suite 100  
Entity Address, City or Town Overland Park  
Entity Address, State or Province KS  
Entity Address, Postal Zip Code 66210  
City Area Code 913  
Local Phone Number 344-9200  
Title of 12(b) Security Common stock, $0.01 par value  
Trading Symbol CMP  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   41,958,348
Entity Central Index Key 0001227654  
Current Fiscal Year End Date --09-30  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Amendment Flag false  
v3.26.1
CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Current assets:    
Cash and cash equivalents $ 74.1 $ 59.7
Receivables, less allowance for credit losses and rebates of $2.8 and $2.2 at March 31, 2026 and September 30, 2025, respectively 223.3 179.6
Inventories, less allowance of $6.0 and $7.7 at March 31, 2026 and September 30, 2025, respectively 178.7 312.0
Other current assets 32.0 20.9
Total current assets 508.1 572.2
Property, plant and equipment, net 748.3 770.1
Intangible assets, net 4.3 23.8
Goodwill 6.0 6.0
Other noncurrent assets 98.6 147.3
Total assets 1,365.3 1,519.4
Current liabilities:    
Accounts payable 100.8 96.0
Accrued salaries and wages 18.2 26.4
Current portion of finance lease liabilities 6.4 7.9
Income taxes payable 0.4 5.6
Accrued interest 13.5 19.0
Accrued expenses and other current liabilities 107.3 110.7
Total current liabilities 246.6 265.6
Long-term debt, net of current portion 713.0 832.2
Finance lease liabilities, net of current portion 5.9 7.6
Deferred income taxes, net 52.1 53.9
Other noncurrent liabilities 73.5 126.0
Commitments and contingencies (Note 8)
Stockholders’ equity:    
Common stock: $0.01 par value, 200,000,000 authorized shares; 42,197,964 issued shares at March 31, 2026 and September 30, 2025 0.4 0.4
Additional paid-in capital 425.7 430.0
Treasury stock, at cost — 240,499 shares at March 31, 2026 and 497,420 shares at September 30, 2025 (3.8) (10.8)
Accumulated deficit (46.3) (77.6)
Accumulated other comprehensive loss (101.8) (107.9)
Total stockholders’ equity 274.2 234.1
Total liabilities and stockholders’ equity $ 1,365.3 $ 1,519.4
v3.26.1
CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Current assets:    
Allowance for credit losses and rebates $ 2.8 $ 2.2
Inventory allowance $ 6.0 $ 7.7
Stockholders’ equity:    
Common stock, par value (in dollars per share) $ 0.01 $ 0.01
Common stock, shares authorized (in shares) 200,000,000 200,000,000
Common stock, shares issued (in shares) 42,197,964 42,197,964
Treasury stock, shares (in shares) 240,499 497,420
v3.26.1
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($)
shares in Thousands, $ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Sales $ 453.2 $ 494.6 $ 849.3 $ 801.8
Gross profit 83.0 76.8 146.2 111.1
Selling, general and administrative expenses 27.0 29.6 53.6 62.9
Loss on impairments 0.0 53.0 0.0 53.0
Other operating income 0.0 (2.7) 0.0 (2.2)
Operating income (loss) 56.0 (3.1) 92.6 (2.6)
Other expense (income):        
Interest income (0.6) (0.2) (0.9) (0.6)
Interest expense 17.9 18.0 36.0 34.9
Gain on foreign exchange, net (5.6) (0.1) (3.5) (5.3)
Loss on sale of business, net 14.6 0.0 14.6 0.0
Loss on extinguishment of debt 0.5 0.0 0.5 0.0
Other expense, net 0.5 1.4 0.8 4.5
Net income (loss) before income taxes 28.7 (22.2) 45.1 (36.1)
Income tax expense 16.0 9.8 13.8 19.5
Net income (loss) $ 12.7 $ (32.0) $ 31.3 $ (55.6)
Basic net income (loss) per common share (in dollars per share) $ 0.30 $ (0.77) $ 0.73 $ (1.34)
Diluted net income (loss) per common share (in dollars per share) $ 0.30 $ (0.77) $ 0.73 $ (1.34)
Weighted-average common shares outstanding (in thousands):        
Basic (in shares) 42,160 41,521 42,105 41,480
Diluted (in shares) 42,357 41,521 42,297 41,480
Shipping and handling cost        
Cost $ 138.0 $ 151.4 $ 250.1 $ 232.0
Product cost        
Cost $ 232.2 $ 266.4 $ 453.0 $ 458.7
v3.26.1
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Statement of Comprehensive Income [Abstract]        
Net income (loss) $ 12.7 $ (32.0) $ 31.3 $ (55.6)
Other comprehensive income (loss):        
Unrealized gain from change in pension obligations, net of tax of $0.0 for both the three months ended March 31, 2026 and March 31, 2025, respectively, and $(0.1) for both the six months ended March 31, 2026 and March 31, 2025, respectively 0.2 0.2 0.4 0.4
Unrealized loss from change in other postretirement benefits, net of tax of $0.0 for the six months ended March 31, 2025 0.0 0.0 0.0 (0.1)
Unrealized (loss) gain on cash flow hedges, net of tax of $0.0 for both the three and six months ended March 31, 2026 and March 31, 2025, respectively (0.7) 1.1 (1.2) 0.8
Unrealized foreign currency translation adjustments (13.2) 2.1 (6.2) (31.2)
Realized loss on foreign currency transactions reclassified into Loss on sale of business, net 13.1 0.0 13.1 0.0
Other comprehensive income (loss) (0.6) 3.4 6.1 (30.1)
Total comprehensive income (loss) $ 12.1 $ (28.6) $ 37.4 $ (85.7)
v3.26.1
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (Parenthetical) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Statement of Comprehensive Income [Abstract]        
Unrealized gain (loss) from change in pension obligations, tax $ 0.0 $ 0.0 $ (0.1) $ (0.1)
Unrealized loss, other postretirement benefits, tax       0.0
Unrealized income (loss) on cash flow hedges, tax $ 0.0 $ 0.0 $ 0.0 $ 0.0
v3.26.1
CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($)
$ in Millions
Total
Common Stock
Additional Paid-In Capital
Treasury Stock
Accumulated (Deficit) Income
Accumulated Other Comprehensive (Loss) Income
Beginning Balance at Sep. 30, 2024 $ 316.6 $ 0.4 $ 420.6 $ (10.2) $ 2.2 $ (96.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Total comprehensive income (loss) (57.1)       (23.6) (33.5)
Shares issued for stock units, net of shares withheld for taxes (0.4)   (0.2) (0.2)    
Stock-based compensation 3.9   3.9      
Ending Balance at Dec. 31, 2024 263.0 0.4 424.3 (10.4) (21.4) (129.9)
Beginning Balance at Sep. 30, 2024 316.6 0.4 420.6 (10.2) 2.2 (96.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Total comprehensive income (loss) (85.7)          
Ending Balance at Mar. 31, 2025 236.5 0.4 426.6 (10.6) (53.4) (126.5)
Beginning Balance at Dec. 31, 2024 263.0 0.4 424.3 (10.4) (21.4) (129.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Total comprehensive income (loss) (28.6)       (32.0) 3.4
Shares issued for stock units, net of shares withheld for taxes (0.7)   (0.5) (0.2)    
Stock-based compensation 2.8   2.8      
Ending Balance at Mar. 31, 2025 236.5 0.4 426.6 (10.6) (53.4) (126.5)
Beginning Balance at Sep. 30, 2025 234.1 0.4 430.0 (10.8) (77.6) (107.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Total comprehensive income (loss) 25.3       18.6 6.7
Shares issued for stock units, net of shares withheld for taxes (1.2)   (0.4) (0.8)    
Stock-based compensation 2.3   2.3      
Ending Balance at Dec. 31, 2025 260.5 0.4 431.9 (11.6) (59.0) (101.2)
Beginning Balance at Sep. 30, 2025 234.1 0.4 430.0 (10.8) (77.6) (107.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Total comprehensive income (loss) 37.4          
Ending Balance at Mar. 31, 2026 274.2 0.4 425.7 (3.8) (46.3) (101.8)
Beginning Balance at Dec. 31, 2025 260.5 0.4 431.9 (11.6) (59.0) (101.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]            
Total comprehensive income (loss) 12.1       12.7 (0.6)
Shares issued for stock units, net of shares withheld for taxes (0.6)   (8.4) 7.8    
Stock-based compensation 2.2   2.2      
Ending Balance at Mar. 31, 2026 $ 274.2 $ 0.4 $ 425.7 $ (3.8) $ (46.3) $ (101.8)
v3.26.1
CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)
$ in Millions
 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Cash flows from operating activities:    
Net income (loss) $ 31.3 $ (55.6)
Adjustments to reconcile net income (loss) to net cash flows provided by operating activities:    
Depreciation, depletion and amortization 54.6 53.3
Amortization of deferred financing costs 2.1 2.6
Non-cash portion of stock-based compensation 4.5 6.7
Deferred income taxes (1.8) 0.8
Unrealized foreign exchange gain, net (3.9) (6.4)
Loss on impairments 0.0 53.0
Net gain from remeasurement of contingent consideration 0.0 (7.9)
Loss on extinguishment of debt 0.5 0.0
Loss on sale of business, net 14.6 0.0
Other, net 1.9 0.6
Changes in operating assets and liabilities:    
Receivables (46.2) (63.8)
Inventories 121.3 183.3
Other assets 40.0 2.0
Accounts payable and accrued expenses and other current liabilities (8.6) 6.4
Other liabilities (49.9) 7.8
Net cash provided by operating activities 160.4 182.8
Cash flows from investing activities:    
Capital expenditures (41.0) (35.8)
Proceeds from sale of business, net of cash and transaction costs 23.2 0.0
Other, net (0.8) (0.1)
Net cash used in investing activities (18.6) (35.9)
Cash flows from financing activities:    
Borrowings under revolving credit facility 47.0 140.3
Repayments under revolving credit facility (47.0) (299.9)
Proceeds from issuance of long-term debt 58.8 62.1
Principal payments on long-term debt (179.6) (12.3)
Payments of deferred financing costs (0.3) (2.4)
Shares withheld to satisfy employee tax obligations (1.7) (1.1)
Other, net (4.5) (3.5)
Net cash used in financing activities (127.3) (116.8)
Effect of exchange rate changes on cash and cash equivalents (0.1) (0.8)
Net change in cash and cash equivalents 14.4 29.3
Cash and cash equivalents, beginning of the year 59.7 20.2
Cash and cash equivalents, end of period 74.1 49.5
Supplemental cash flow information:    
Interest paid, net of amounts capitalized 39.5 34.2
Income taxes paid, net of refunds 31.8 25.3
Non-cash activities:    
Right-of-use assets obtained in exchange for new operating lease liabilities 5.9 13.3
Right-of use assets obtained in exchange for new finance lease liabilities $ 0.0 $ 5.8
v3.26.1
ACCOUNTING POLICIES AND BASIS OF PRESENTATION
 6 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
ACCOUNTING POLICIES AND BASIS OF PRESENTATION ACCOUNTING POLICIES AND BASIS OF PRESENTATION
Compass Minerals International, Inc. (“CMI”), through its subsidiaries (collectively, the “Company”), is a leading global provider of essential minerals focused on safely delivering where and when it matters to help solve nature’s challenges for customers and communities. The Company’s salt products help keep roadways safe during winter weather and are used in numerous other consumer, industrial, chemical and agricultural applications. Its plant nutrition business is the leading North American producer of sulfate of potash (“SOP”), which is used in the production of specialty fertilizers for high-value crops and turf and helps improve the quality and yield of crops, while supporting sustainable agriculture. The Company’s principal products are salt, consisting of sodium chloride and magnesium chloride, and SOP. The Company’s production sites are located in the United States (“U.S.”), Canada and the United Kingdom (“UK”). The Company also provides records management services in the UK. Except where otherwise noted, references to North America include only the continental U.S. and Canada, and references to the UK include only England, Scotland and Wales. References to “Compass Minerals,” “our,” “us” and “we” refer to CMI and its consolidated subsidiaries.
 
CMI is a holding company with no significant operations other than those of its wholly-owned subsidiaries. The consolidated financial statements include the accounts of CMI and its wholly-owned domestic and foreign subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.

The accompanying condensed consolidated balance sheet as of September 30, 2025, which was derived from audited financial statements, and the unaudited condensed consolidated financial statements (“Condensed Consolidated Financial Statements”) have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete consolidated financial statements. As a result, these Condensed Consolidated Financial Statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended September 30, 2025. In the opinion of management, these interim financial statements reflect all adjustments, consisting of normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and results of operations.
 
Accounting Pronouncements Issued Not Yet Adopted

Income Tax Disclosures. In December 2023, the Financial Accounting Standards Board (“FASB”) issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which updates income tax disclosures by requiring consistent categories and additional disaggregation of information in the rate reconciliation and income taxes paid by jurisdiction. The ASU is effective for fiscal years beginning after December 15, 2024, and is effective for the Company beginning in the annual report for the fiscal year ended September 30, 2026. Early adoption is permitted. The amendments should be applied prospectively; however, retrospective application is permitted. Management is currently evaluating this ASU to determine its impact on the Company’s disclosures.

Disaggregation of Income Statement Expenses. In November 2024, the FASB issued amended guidance related to disclosure of disaggregated expenses (“ASU 2024-03”). This amendment requires public business entities to provide detailed disclosures in the notes to financial statements disaggregating specific expense categories, including purchases of inventory, employee compensation, depreciation, depletion, and intangible asset amortization, as well as certain other disclosures to provide enhanced transparency into the nature and function of expenses. This guidance is effective for annual periods beginning with the Company’s annual report for the fiscal year ended September 30, 2028, and interim periods following annual adoption, with early adoption permitted. This guidance will be applied on a prospective basis with retrospective application permitted. Management is currently evaluating ASU 2024-03 to determine its impact on the Company’s disclosures.

Interim Reporting. In December 2025, the FASB issued ASU 2025-11, Interim Reporting (Topic 270): Narrow-Scope Improvements (“ASU 2025-11”), to improve the guidance for interim reporting and clarify when that guidance is applicable. This ASU provides a comprehensive list of required interim disclosures and also requires entities to disclose events since the end of the last annual reporting period that have a material impact on the entity. ASU 2025-11 is effective for interim reporting periods within annual reporting periods beginning after December 15, 2027. For the Company, the guidance becomes effective in the first interim period of the fiscal year ended September 30, 2029. Early adoption is permitted. Management is currently evaluating ASU 2025-11 to determine its impact on the Company’s disclosures.
v3.26.1
REVENUES
 6 Months Ended
Mar. 31, 2026
Revenue from Contract with Customer [Abstract]  
REVENUES REVENUES
Disaggregation of Revenue

Sales is disaggregated in the following table by timing of revenue recognition (in millions):
 Three Months Ended
March 31,		Six Months Ended
March 31,
 2026202520262025
Timing of revenue recognition:
Products and services transferred at a point in time$450.4 $492.0 $843.7 $796.6 
Products and services transferred over time(a)
2.8 2.6 5.6 5.2 
Total sales$453.2 $494.6 $849.3 $801.8 
(a)     Amounts include records management business utilizing excavated areas of its Winsford salt mine with one other location in London, England.

For disaggregation of sales by segment and type, see Note 9. Operating Segments.

Receivables

The following table provides the balances of receivables (in millions):
 March 31,
2026		September 30,
2025
Current assets:
Receivables related to contracts with customers
$170.4 $127.3 
Miscellaneous receivables(a)
52.9 52.3 
Total receivables
$223.3 $179.6 
(a)Refer to Note 8. Commitments and Contingencies for additional information.

Deferred Revenue

Deferred revenue represents collections under contracts before the related product or service is transferred to the customer. The portion of deferred revenue that is anticipated to be recognized as revenue during the succeeding twelve-month period is recorded in Accrued expenses and other current liabilities in the Condensed Consolidated Balance Sheets. Deferred revenue included in Accrued expenses and other current liabilities as of March 31, 2026 and September 30, 2025 was approximately $0.8 million and $1.6 million, respectively. Of the total deferred revenues in the Condensed Consolidated Balance Sheet as of September 30, 2025 that were reclassified to revenue as the result of performance obligations being satisfied during the six months ended March 31, 2026 was $0.8 million.
v3.26.1
DISPOSITIONS
 6 Months Ended
Mar. 31, 2026
Discontinued Operations and Disposal Groups [Abstract]  
DISPOSITIONS DISPOSITIONS
Sale and Disposition of Wynyard SOP Business

On February 3, 2026, the Company entered into a share purchase agreement (the “Share Purchase Agreement”) to sell its sulfate of potash specialty fertilizer (“SOP”) business in Wynyard, Saskatchewan, Canada. The Share Purchase Agreement provided for total consideration of approximately $30.8 million, prior to indebtedness and working capital adjustments totaling approximately $2.1 million.

The transaction closed on March 1, 2026. At closing, the Company received cash proceeds of $23.2 million, net of (i) $3.9 million ($5.2 million denominated in Canadian dollars (“CAD”)) placed in escrow, (ii) $1.3 million of cash on hand transferred to the buyer, and (iii) $0.3 million of transaction costs. The escrow agreement provides for potential purchase price adjustments related to indemnification of claims. Of the escrowed amount, approximately CAD $3.3 million is scheduled to be released on March 1, 2027, and the remaining CAD $1.9 million is scheduled to be released on March 1, 2028, in each case plus accrued interest and net of any amounts deducted pursuant to the terms of the escrow agreement.
As a result of the transaction, the Company recorded a pre-tax Loss on sale of business, net, of $14.6 million, which included $13.1 million of cumulative foreign currency translation adjustments reclassified from Accumulated other comprehensive loss, for both the three and six months ended March 31, 2026. Prior to the sale, the results of the Wynyard SOP business were included in the Company’s Plant Nutrition operating segment. The transaction supports the Company’s ongoing balance sheet strengthening and debt-reduction initiatives.

In connection with the transaction, the Company entered into a transition services agreement with the purchaser that is designed to facilitate the orderly transfer of the operations, including administrative services, which are generally to be provided within 12 months after the closing date. This agreement was not material and does not confer upon the Company the ability to influence the operating or financial policies of the Wynyard SOP business subsequent to March 1, 2026.

As of the March 1, 2026 disposal date, the business had net assets with a carrying value of $30.2 million, which included $1.3 million of cash and cash equivalents, $19.1 million of net intangible assets, $9.0 million of property, plant and equipment (“PP&E”), and $0.8 million of net other assets and liabilities.

Fortress Exit

On March 25, 2025, the Company took measures to align the Company’s cost structure to its current business needs as part of a larger strategic refocus to improve the profitability of the Company’s core Salt and Plant Nutrition businesses. Specifically, the Company began the process of exiting the Fortress North America, LLC (“Fortress”) fire retardant business and terminating the employment of all Fortress employees. The results of operations of Fortress were included in Corporate and Other segment.

Impairment. As a result of the above items impacting Fortress, the Company determined that there were indicators of impairment with the associated Fortress intangible assets. Accordingly, the Company performed an impairment assessment of its customer relationships and trade name intangible assets, and their fair value was determined to be zero using an income approach in accordance with ASC 820, Fair Value Measurement, utilizing Level 3 inputs. As a result, the Company recorded full impairment losses of $52.9 million related to customer relationships and $0.1 million related to the trade name, in Loss on impairments, for both the three and six months ended March 31, 2025.

Additionally, the Company performed an impairment test on the remaining Fortress asset group (including PP&E, inventory, and in-process research and development (“IPR&D”)), with a carrying amount of $19.7 million. The impairment test under ASC 360, Property, Plant, and Equipment, compared the asset group’s undiscounted cash flows to its carrying amount. The Company determined the fair value of the asset group using a market approach under ASC 820, Fair Value Measurement (Level 2 inputs). The asset group (PP&E, inventory, and IPR&D) was not impaired as its fair value, based on market indications approximated or exceeded its carrying value. The fair value estimates involved significant estimates and assumptions.

Contingent Consideration. In connection with the acquisition of Fortress on May 5, 2023, the Company entered into a contingent consideration arrangement for up to $28 million to be paid in cash and/or Compass Minerals common stock upon the achievement of certain performance measures over the next five years, and a cash earn-out based on volumes of certain Fortress fire retardant products sold over a 10-year period. The carrying value of the contingent consideration at December 31, 2024 was $7.9 million, with $0.1 million included in Accrued expenses and other current liabilities and $7.8 million included in Other noncurrent liabilities. Given the business ceased operations and had no future expected cash flows, the carrying value of the contingent consideration was reduced to zero as of March 31, 2025. For both the three and six months ended March 31, 2025, the Company recorded income, included in Other operating expense (income) of $7.9 million.
v3.26.1
INVENTORIES
 6 Months Ended
Mar. 31, 2026
Inventory Disclosure [Abstract]  
INVENTORIES INVENTORIES
 
Inventories consist of the following (in millions):
 March 31,
2026		September 30,
2025
Finished goods$76.5 $219.1 
Work in process5.9 5.9 
Raw materials and supplies(a)
96.3 87.0 
Total inventories$178.7 $312.0 
(a)Excludes certain raw materials and supplies of $32.9 million and $33.0 million as of March 31, 2026 and September 30, 2025, respectively, that are not expected to be consumed within the next twelve months, included in Other noncurrent assets in the Condensed Consolidated Balance Sheets.
v3.26.1
PROPERTY, PLANT AND EQUIPMENT, NET
 6 Months Ended
Mar. 31, 2026
Property, Plant and Equipment [Abstract]  
PROPERTY, PLANT AND EQUIPMENT, NET PROPERTY, PLANT AND EQUIPMENT, NET
 
Property, plant and equipment, net, consists of the following (in millions):
 March 31,
2026		September 30,
2025
Land, buildings and structures, and leasehold improvements(a)
$543.3 $554.1 
Machinery and equipment(a)
1,156.7 1,154.9 
Office furniture and equipment23.4 23.9 
Mineral interests168.6 169.1 
Construction in progress56.7 51.6 
 1,948.7 1,953.6 
Less: accumulated depreciation, depletion, and amortization(1,200.4)(1,183.5)
Property, plant and equipment, net$748.3 $770.1 
(a)    Includes finance lease right-of-use assets.

The following table provides supplemental non-cash activities (in million):
Six Months Ended
March 31,
 20262025
Purchases of Property, plant and equipment in Accounts payable$8.6 $6.2 
Purchases of Property, plant and equipment in Accrued expenses and other current liabilities3.8 5.1 
Transfers of Property, plant and equipment from Inventory6.1 3.7 
v3.26.1
INCOME TAXES
 6 Months Ended
Mar. 31, 2026
Income Tax Disclosure [Abstract]  
INCOME TAXES INCOME TAXES
The Company’s effective income tax rate differs from the U.S. statutory federal income tax rate primarily due to U.S. statutory depletion, state income taxes (net of federal tax benefit), nondeductible executive compensation over $1 million, foreign income, mining and withholding taxes, base erosion and anti-abuse tax, and valuation allowances recorded on deferred tax assets.

The effective tax rates applied to the six months ended March 31, 2026 were determined by excluding the U.S. losses from the overall estimated annual effective tax rate computations and a separate estimated annual effective tax rate was computed and applied to the ordinary U.S. losses.

Management assesses the available positive and negative evidence to estimate whether sufficient future taxable income will be generated to permit use of the existing deferred tax assets. A significant piece of objective negative evidence evaluated was the cumulative loss incurred in the U.S. over the three-year period ended March 31, 2026. Such objective evidence limits the ability to consider other subjective evidence, such as the Company’s projections for future income. On the basis of this evaluation, an additional valuation allowance of $0.1 million has been recorded to recognize only the portion of the U.S. deferred tax assets that is more likely than not to be realized. The amount of the deferred tax assets considered realizable, however, could be adjusted if objective negative evidence in the form of cumulative losses is no longer present and additional weight is given to subjective evidence such as the Company’s projections for income.

As of both March 31, 2026 and September 30, 2025, the Company had $80.5 million of gross federal net operating loss (“NOL”) carryforwards that have no expiration date and $7.1 million at both March 31, 2026 and September 30, 2025 of net operating tax-effected state NOL carryforwards which expire beginning in 2031.

In November 2025, the Company reached a settlement with a Canadian provincial tax authority regarding a tax dispute for fiscal years 2002 through 2018. The Canadian provincial tax authority had challenged tax positions claimed by one of the
Company’s Canadian subsidiaries and issued tax reassessments for fiscal years 2002 through 2020. The reassessments were the result of ongoing audits and totaled $209.8 million, including interest as of September 30, 2025.

The settlement resolved the dispute for tax years 2002 through 2018. In connection with the settlement, the Company also revised its mining tax calculations for tax years subsequent to 2018 consistent with the principles agreed to in the settlement agreement. The Company is in the process of amending the relevant tax returns to obtain the associated federal and provincial refunds. The total net expected cash outlay, after taking into account expected federal refunds and deductions associated with the agreed upon tax and interest as well as estimated subsequent tax year impacts is $8.2 million. Additionally, the settlement and other updates to uncertain tax positions resulted in an overall tax benefit of $4.0 million, for the six months ended March 31, 2026.

The Company previously paid $35.8 million over a period of several years to the Canadian tax authorities as a deposit, which was recorded in Other noncurrent assets in the Consolidated Balance Sheets. The deposit was previously required to be paid by the Company to proceed with future appeals or litigation and was subsequently applied to the amount due at settlement. The remaining settlement amount of $24.8 million related to tax years 2002 through 2018 was paid in November 2025.

The additional impacts of the settlement on the Consolidated Balance Sheets at March 31, 2026, as compared to September 30, 2025, included an increase of $21.9 million in Other current assets, due to expected federal refunds from amended returns to be filed; a decrease in Other noncurrent assets of $47.1 million, primarily due to the application of the deposit to the amount of the total settlement; and a decrease in Other noncurrent liabilities of $54.0 million, due to the change in liabilities for uncertain tax positions. With the settlement, the performance bonds of $157.4 million posted as collateral for the 2002 through 2018 period were released.

On July 4, 2025, the U.S. enacted a budget reconciliation package known as the “One Big Beautiful Bill Act of 2025” (“OBBBA”), which includes both tax and non-tax provisions. While the Company is benefiting from the relaxing of interest deduction limitations, the Company does not view the legislation to significantly impact its income tax profile.
v3.26.1
LONG-TERM DEBT AND FINANCE LEASE LIABILITIES
 6 Months Ended
Mar. 31, 2026
Debt Disclosure [Abstract]  
LONG-TERM DEBT AND FINANCE LEASE LIABILITIES LONG-TERM DEBT AND FINANCE LEASE LIABILITIES
 
Total long-term carrying value of debt and finance lease liabilities consists of the following (in millions):
 March 31,
2026		September 30,
2025
Secured Debt:
Revolving Credit Facility due May 2028$— $— 
Subordinated Debt:
8.00% Senior Notes due July 2030
650.0 650.0 
6.75% Senior Notes due December 2027
— 150.0 
Accounts Receivable Securitization Facility75.0 45.8 
Total principal amount of debt725.0 845.8 
Finance lease liabilities12.3 15.5 
Unamortized deferred financing costs(12.0)(13.6)
Total carrying value of debt and finance lease liabilities725.3 847.7 
Current portion of finance lease liabilities(6.4)(7.9)
Total long-term carrying value of debt and finance lease liabilities$718.9 $839.8 

8.00% Senior Notes due 2030

On June 16, 2025, the Company issued $650.0 million aggregate principal amount of its 8.00% Senior Notes due 2030 in a private offering, pursuant to an indenture, dated June 16, 2025 (the “2030 Notes”), among the Company, the subsidiary guarantors named therein and Computershare Trust Company, N.A., as trustee. The 2030 Notes are senior unsecured obligations, with interest payable semi-annually on January 1 and July 1. The 2030 Notes are guaranteed by certain of the Company’s domestic subsidiaries. The 2030 Notes will mature on July 1, 2030. The Company incurred $13.0 million in deferred financing costs, including arrangement, legal and other fees, and will be amortized to interest expense over the 5-year term of the 2030 Notes.
The indenture governing the 2030 Notes contains covenants limiting other indebtedness, dividends, purchases or redemptions of stock, transactions with affiliates, and mergers and sales of assets.

6.75% Senior Notes due 2027

In November 2019, the Company issued $500 million aggregate principal amount of its 6.75% Senior Notes due December 2027 (the “2027 Notes”). The 2027 Notes were unsecured obligations and were guaranteed by certain of the Company’s domestic subsidiaries. Interest on the 2027 Notes was due semi-annually on June 1 and December 1. The 2027 Notes were scheduled to mature on December 1, 2027 and were subordinated to all existing and future indebtedness. The indenture governing the 2027 Notes contained covenants limiting other indebtedness, dividends, purchases or redemptions of stock, transactions with affiliates, and mergers and sales of assets.

On June 17, 2025, the Company redeemed $350.0 million of the 2027 Notes, reducing the aggregate outstanding principal balance to $150.0 million.

On March 30, 2026, the Company redeemed in full the remaining $150.0 million outstanding 2027 Notes using cash on hand at 100% of principal plus accrued interest through, but excluding, the redemption date. The Company recorded a $0.5 million loss on extinguishment of debt related to the write-off of deferred financing costs, during the three and six months ended March 31, 2026.

Accounts Receivable Securitization Facility

On June 30, 2020, certain of the Company’s U.S. subsidiaries entered into a committed revolving accounts receivable financing facility (the “AR Facility”) of up to $100.0 million with PNC Bank, National Association (“PNC”), as administrative agent and lender, and PNC Capital Markets, LLC, as structuring agent. The AR Facility was further amended by the First Amendment to the AR Facility, dated as of June 27, 2022, the Second Amendment to the AR Facility, dated as of January 31, 2023, the Third Amended to the AR Facility, dated as of March 27, 2024 (extending the AR facility to March 2027), the Fourth Amended to the AR Facility, dated as of August 12, 2024, and the Fifth Amendment to the AR Facility, dated as of September 13, 2024.

On March 19, 2026, certain of the Company’s U.S. subsidiaries entered into a Sixth Amendment to its AR Facility, extending the facility to March 2029.

In connection with the AR Facility, one of the Company’s U.S. subsidiaries, from time to time, sells and contributes receivables and certain related assets to a special purpose entity and wholly-owned U.S. subsidiary of the Company (the “SPE”). The SPE finances its acquisition of the receivables by obtaining secured loans from PNC and the other lenders party to a receivables financing agreement. A U.S. subsidiary of the Company services the receivables on behalf of the SPE for a fee. In addition, the Company has agreed to guarantee the performance by its subsidiaries. The Company and its subsidiaries do not guarantee the loan principal or interest under the receivables financing agreement or the collectability of the receivables under the AR Facility.

Amended and Restated Credit Agreement

The Company is party to its 2023 Credit Agreement, dated April 20, 2016 (as amended and restated as of November 26, 2019, as amended and restated as of May 5, 2023, as further amended by the First Amendment to the Credit Agreement, dated as March 27, 2024, the Second Amendment to the Credit Agreement, dated as of August 12, 2024, the Third Amendment to the Credit Agreement, dated as of September 13, 2024, the Fourth Amendment to the Credit Agreement, dated as of December 12, 2024, and the Fifth Amendment, dated as of June 16, 2025), (together the “Amended and Restated 2023 Credit Agreement”).

The Fifth Amendment, dated as of June 16, 2025 under the Amended and Restated 2023 Credit Agreement, among other things, fixed the aggregate revolving commitments at $325.0 million. The revolving credit facility under the Amended and Restated 2023 Credit Agreement is secured by substantially all existing and future U.S. assets of the Company, the Goderich mine in Ontario, Canada, and capital stock of certain subsidiaries.

As of March 31, 2026, the Company had no borrowings outstanding under its revolving credit facility. Also, as of March 31, 2026, outstanding letters of credit totaling $20.2 million further reduced the available borrowing capacity under the Company’s $325.0 million revolving credit facility to $304.8 million. Borrowings, if any, accrue interest at a rate per annum based on, at the Company’s option, the Adjusted Term SOFR Rate, Adjusted EURIBO Rate, Canadian Prime Rate, or Sterling Overnight Index Average, plus applicable margin.
v3.26.1
COMMITMENTS AND CONTINGENCIES
 6 Months Ended
Mar. 31, 2026
Commitments and Contingencies Disclosure [Abstract]  
COMMITMENTS AND CONTINGENCIES COMMITMENTS AND CONTINGENCIES
The Company is subject to legal and administrative proceedings, environmental remediation liabilities, and claims of various types from the ordinary course of the Company’s business. If management believes that a loss arising from these actions is probable and can reasonably be estimated, the Company records the amount of the loss or the minimum estimated liability when the loss is estimated using a range and no point is more probable than another. As additional information becomes available, any potential liability related to these actions is assessed and the estimates are revised, if necessary.

Management cannot predict the outcome of legal claims and proceedings with certainty. Nevertheless, management believes that the outcome of legal proceedings and claims, which are pending or known to be threatened, even if determined adversely, will not, individually or in the aggregate, have a material adverse effect on the Company’s results of operations, cash flows or financial position given current insurance coverage, except as otherwise described in this Note 8.

Beginning on February 1, 2023, two shareholder derivative lawsuits were filed in the United States District Court for the District of Kansas against certain directors and executives of the Company, purportedly on behalf of the Company, alleging breaches of fiduciary duties arising from materially false and misleading statements and omissions during the period from October 30, 2017 to October 21, 2022. The court consolidated the actions on February 28, 2025. On October 14, 2025, the court approved a settlement resolving the consolidated derivative action, pursuant to which the Company agreed to adopt certain corporate governance reforms, and insurers for the defendant directors and executives paid the full amount of the awarded legal fees and expenses in accordance with the court’s order and the settlement agreement.

On April 24, 2024, a putative securities class action was filed in the United States District Court for the District of Kansas against the Company and certain individuals, alleging materially false and misleading statements during the period from February 8, 2023 to March 25, 2024, regarding Fortress North America, the Company’s former fire retardant business. An amended complaint was filed on February 10, 2025. On January 7, 2026, the court granted final approval of a settlement resolving the matter for $4.9 million, which was consented to by the Company’s insurers, with approximately $1.0 million paid by the Company.

Beginning on October 30, 2024, two shareholder derivative lawsuits were filed against certain current and former officers and directors of the Company, purportedly on behalf of the Company, alleging that misleading statements and omissions were made regarding the Company’s fire retardant business during the period from November 29, 2023 to March 22, 2024. The court consolidated the actions on June 3, 2025, and an amended consolidated complaint was filed on July 30, 2025, which added an additional defendant and asserted additional claims. On February 20, 2026, the court granted final approval of a settlement resolving the derivative actions. Pursuant to the settlement, the Company agreed to implement certain corporate governance reforms, and the Company’s insurers agreed to pay legal fees and expenses to plaintiffs’ counsel.

On October 25, 2024, the Company issued a recall for specific production lots of food-grade salt produced at its Goderich Plant following a customer report of a non-organic, foreign material in its product. The Company subsequently expanded the voluntary recall to include food products from the Goderich Plant between September 18, 2024 and November 6, 2024. The Company followed recall protocol and notified its BRCGS Global Standard for Food Safety certifying body, the Canadian Food Inspection Agency (“CFIA”) and the U.S. Food and Drug Administration (“FDA”). The Company has completed its investigation and continues to assess the scope and magnitude of asserted and potential customer claims related to the recall. At this time, based on currently available information and its applicable insurance coverage, the Company does not believe any incremental losses will have a material adverse effect on its results of operations or cash flows in future periods. The recall in the United States, supervised by the FDA, is complete, and the matter is closed with FDA. The CFIA has conducted a follow-up inspection of the Goderich Plant to verify compliance with regulatory requirements and identified no non-compliances.

In March 2026, the Company submitted a remediation plan to the State of Utah to address a diesel release from underground piping at a fueling station located at its Ogden, Utah facility. As of March 31, 2026, the Company recorded an estimated liability of $2.8 million, included in Accrued expenses and other current liabilities and estimated insurance recoveries of $2.3 million, included in Receivables related to this matter. Environmental liabilities may decline as remediation spending occurs.
As of March 31, 2026 and September 30, 2025, the Company recorded liabilities of $45.6 million and $51.8 million, respectively, included in Accrued expenses and other current liabilities, $4.4 million and $0.0 million, respectively, included in Other noncurrent liabilities, and estimated insurance recoveries of $45.3 million and $47.0 million, respectively, included in Receivables, in the Condensed Consolidated Balance Sheets associated with the legal, environmental, and product recall matters described above.
v3.26.1
OPERATING SEGMENTS
 6 Months Ended
Mar. 31, 2026
Segment Reporting [Abstract]  
OPERATING SEGMENTS OPERATING SEGMENTS
 
The Company’s reportable segments are strategic business units that offer different products and services, and each business requires different technology and marketing strategies. The Company has presented two reportable segments in its Condensed Consolidated Financial Statements: Salt and Plant Nutrition. The Salt segment produces and markets salt, consisting primarily of sodium chloride and magnesium chloride, for use in road deicing for winter roadway safety and for dust control, food processing, water softening and other consumer, agricultural and industrial applications. The Plant Nutrition segment produces and markets various grades of SOP. On March 1, 2026, the Company sold its SOP business in Wynyard, Saskatchewan, Canada included in the Plant Nutrition segment, see Note 3. Dispositions for further information. The results of operations for the Company’s records management businesses are included in Corporate and Other in the tables below.

The chief operating decision maker (“CODM”) is the Company’s President and Chief Executive Officer. The primary measure of segment profit or loss used by the CODM to regularly evaluate performance, make key operating decisions and determine resource allocation of and among each operating segment is operating income.

Segment information is as follows (in millions):
Three Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Sales to external customers(b)
$382.6 $67.0 $3.6 $453.2 
Intersegment sales— 2.0 (2.0)— 
Shipping and handling cost128.7 9.3 — 138.0 
Product cost181.1 48.7 2.4 232.2 
Gross profit72.8 9.0 1.2 83.0 
Selling, general and administrative expenses7.6 1.4 18.0 27.0 
Operating income (loss)65.2 7.6 (16.8)56.0 
Other Segment Disclosures:
Depreciation, depletion and amortization18.0 9.3 0.9 28.2 
Loss on sale of business, net(d)
— 14.6 — 14.6 
Total assets (as of end of period)825.3 338.2 201.8 1,365.3 

Three Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Sales to external customers(b)
$432.7 $58.3 $3.6 $494.6 
Intersegment sales— 2.3 (2.3)— 
Shipping and handling cost141.9 9.5 — 151.4 
Product cost214.3 48.6 3.5 266.4 
Gross profit76.5 0.2 0.1 76.8 
Selling, general and administrative expenses9.1 2.0 18.5 29.6 
Loss on impairments(c)
— — 53.0 53.0 
Other operating expense (income)0.5 — (3.2)(2.7)
Operating income (loss)66.9 (1.8)(68.2)(3.1)
Other Segment Disclosures:
Depreciation, depletion and amortization17.4 7.4 1.7 26.5 
Total assets (as of end of period)959.2 365.7 207.0 1,531.9 
Six Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Sales to external customers(b)
$714.1 $127.8 $7.4 $849.3 
Intersegment sales— 3.0 (3.0)— 
Shipping and handling cost232.5 17.6 — 250.1 
Product cost353.1 95.0 4.9 453.0 
Gross profit128.5 15.2 2.5 146.2 
Selling, general and administrative expenses14.2 2.2 37.2 53.6 
Operating income (loss)114.3 13.0 (34.7)92.6 
Other Segment Disclosures:
Depreciation, depletion and amortization36.1 16.7 1.8 54.6 
Loss on sale of business, net(d)
— 14.6 — 14.6 
Capital expenditures31.0 9.2 0.8 41.0 

Six Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Sales to external customers(b)
$674.9 $119.7 $7.2 $801.8 
Intersegment sales— 5.5 (5.5)— 
Shipping and handling cost213.2 18.8 — 232.0 
Product cost348.4 103.0 7.3 458.7 
Gross profit (loss)113.3 (2.1)(0.1)111.1 
Selling, general and administrative expenses16.5 2.8 43.6 62.9 
Loss on impairments(c)
— — 53.0 53.0 
Other operating expense (income)0.5 — (2.7)(2.2)
Operating income (loss)96.3 (4.9)(94.0)(2.6)
Other Segment Disclosures:
Depreciation, depletion and amortization34.9 14.9 3.5 53.3 
Capital expenditures27.5 6.2 2.1 35.8 

Disaggregated revenue by product type is as follows (in millions):
Three Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$278.9 $— $— $278.9 
Consumer & Industrial Salt103.7 — — 103.7 
SOP— 69.0 — 69.0 
Eliminations & Other— (2.0)3.6 1.6 
Sales to external customers$382.6 $67.0 $3.6 $453.2 
Three Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$324.8 $— $— $324.8 
Consumer & Industrial Salt107.9 — — 107.9 
SOP— 60.6 — 60.6 
Eliminations & Other— (2.3)3.6 1.3 
Sales to external customers$432.7 $58.3 $3.6 $494.6 

Six Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$489.7 $— $— $489.7 
Consumer & Industrial Salt224.4— — 224.4 
SOP— 130.8 — 130.8 
Eliminations & Other— (3.0)7.4 4.4 
Sales to external customers$714.1 $127.8 $7.4 $849.3 

Six Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$462.9 $— $— $462.9 
Consumer & Industrial Salt212.0 — — 212.0 
SOP— 125.2 — 125.2 
Eliminations & Other— (5.5)7.2 1.7 
Sales to external customers$674.9 $119.7 $7.2 $801.8 
(a)Corporate and Other includes corporate entities, records management operations and other incidental operations and eliminations. Operating income (loss) for Corporate and Other includes indirect corporate overhead, including costs for general corporate governance and oversight, as well as costs for human resources, information technology, legal and finance functions.
(b)Sales to external customers are net of intersegment sales.
(c)The Company recorded a pre-tax Loss on sale of business, net, of $14.6 million, which included $13.1 million of cumulative foreign currency translation adjustments reclassified from Accumulated other comprehensive loss, for both the three and six months ended March 31, 2026.
(d)The Company recorded an impairment loss of $53.0 million related to the exit of the Fortress fire retardant business for both the three and six months ended March 31, 2025.
(e)For the three and six months ended March 31, 2025, the Company recorded costs of $0.9 million and $1.8 million, respectively, related to a recall of food-grade salt produced at its Goderich plant.
(f)For the three and six months ended March 31, 2025, the Company incurred severance and related charges of $4.0 million, due to a reduction in workforce, changes to executive leadership and additional restructuring costs related to the exit of the Fortress fire retardant business.
v3.26.1
STOCKHOLDERS’ EQUITY AND EQUITY INSTRUMENTS
 6 Months Ended
Mar. 31, 2026
Equity [Abstract]  
STOCKHOLDERS’ EQUITY AND EQUITY INSTRUMENTS STOCKHOLDERS’ EQUITY AND EQUITY INSTRUMENTS
Equity Compensation Awards

The 2020 Incentive Award Plan (as amended from time to time, the “2020 Plan”) provides for grants of equity awards to executive officers, other employees and directors, including restricted stock units (“RSUs”), performance stock units (“PSUs”), stock options, deferred stock units (“DSUs”) and other equity-based awards.

Stock-based compensation expense recorded in selling, general and administrative expenses in the Condensed Consolidated Statements of Operations was $2.2 million and $2.8 million for the three months ended March 31, 2026 and March 31, 2025, respectively, and $4.5 million and $6.7 million for the six months ended March 31, 2026 and March 31, 2025, respectively. As of March 31, 2026, there was approximately $12.7 million of total estimated unrecognized compensation cost, assuming attainment of the performance target estimates, related to stock-based compensation arrangements expected to be recognized over a weighted average period of approximately 1.7 years.
Non-Employee Director Compensation. Non-employee directors may elect to receive quarterly fees payable for their service in cash, common stock, or defer all or a portion of such fees into DSUs, equivalent to the value of the Company’s common stock. During the six months ended March 31, 2026, common shares of 8,971 were issued from treasury shares for director compensation related to quarterly fees payable and 4,076 deferred stock units. Annual non-employee director equity compensation is granted in the form of RSUs or DSUs at their election and will vest on the earlier of the day immediately preceding the Issuer's next annual meeting (as long as the meeting is held at least 50 weeks from the grant date) and the first anniversary of the grant date. In relation to these annual fees, the Company granted 33,068 RSUs and 16,982 DSUs to directors during the six months ended March 31, 2026. Additionally, as dividends are declared on the Company’s common stock, these deferred stock units are entitled to accrete dividends in the form of additional units based on the stock price on the dividend payment date. Accumulated deferred stock units are distributed in the form of Company common stock at a future specified date or following resignation from the Board of Directors, based upon the director’s annual election.

RSUs. During the six months ended March 31, 2026, the Company granted 478,287 RSUs which vest after one to three years of service entitling the holders to one share of common stock for each vested RSU. The unvested RSUs do not have voting rights but are entitled to receive non-forfeitable dividends or other distributions that may be declared on the Company’s common stock equal to the per-share dividend declared. The closing stock price on the date of each grant was used to determine the fair value of RSUs.

PSUs. During the six months ended March 31, 2026, the Company granted 182,071 PSUs based upon certain performance criteria and metrics (“2026 Scorecard PSUs”). The actual number of shares of common stock that may be earned with respect to 2026 Scorecard PSUs is calculated based upon the attainment of certain thresholds for free cash flow and return on capital employed during each year of the three-year performance period and may range from 0% to 200% for each measure. Additionally, a modifier will increase or decrease the payout by 20% based upon relative total shareholder return against the Company’s peer group.

To estimate the fair value of the 2026 Scorecard PSUs on the grant date, the Company used a Monte-Carlo simulation model. This model uses historical stock prices to estimate expected volatility and the Company’s correlation to the peer group. The input for the expected stock price volatility was 48%. In addition, the Company used inputs for the risk-free rate of 3.5%, expected dividend yield of 0%, and the Company’s closing stock price on the grant date to estimate the fair value of the 2026 Scorecard PSUs. The Company will adjust the expense of the 2026 Scorecard PSUs based upon its estimate of the number of shares that will ultimately vest at each interim date during the vesting period.

Options. Substantially all of the stock options granted vest ratably, in tranches, over a four-year service period. Unexercised options expire after seven years. Options do not have dividend or voting rights. Upon vesting, each option can be exercised to purchase one share of the Company’s common stock.

The following table summarizes stock-based compensation activity during the six months ended March 31, 2026:
 Stock OptionsRSUs
PSUs(a)
 NumberWeighted-average
exercise price		NumberWeighted-average
fair value		NumberWeighted-average
fair value
Outstanding at September 30, 2025
107,261 $63.43 828,922 $15.34 316,480 $16.89 
Granted— — 478,287 18.47 182,071 19.37 
Released from restriction(b)
— — (318,033)15.69 — — 
Cancelled/expired(794)67.50 (15,573)24.43 — — 
Outstanding at March 31, 2026
106,467 $63.40 973,603 $16.63 498,551 $17.80 
(a)Until the performance period is completed, PSUs are included in the table at the target level at their grant date and at that target level represents one share of common stock per PSU.
(b)The Company paid taxes for restricted unit withholdings of approximately $1.7 million during the six months ended March 31, 2026.
Accumulated Other Comprehensive Loss (“AOCL”)

The following table presents the change in AOCL by component (in millions):

Six Months Ended March 31, 2026(a)
Gains and (Losses) on Cash Flow HedgesDefined Benefit PensionOther Post-Employment BenefitsForeign CurrencyTotal
Beginning balance$(0.8)$(6.3)$1.8 $(102.6)$(107.9)
Other comprehensive loss before reclassifications(b)
(1.7)— — (6.2)(7.9)
Amounts reclassified from AOCL(c)(d)(e)
0.5 0.4 — 13.1 14.0 
Net current period other comprehensive income (loss)(1.2)0.4 — 6.9 6.1 
Ending balance$(2.0)$(5.9)$1.8 $(95.7)$(101.8)
(a)With the exception of the CTA and cash flow hedges, for which no tax effect is recorded, the changes in the components of AOCL presented in the tables above are reflected net of applicable income taxes.
(b)The Company recorded foreign exchange gain of $0.2 million in the six months ended March 31, 2026, in AOCL related to intercompany notes which were deemed to be of a long-term investment nature.
(c)Cash flow hedge amounts reclassified from AOCL to expense (income) were included in Product cost in the Condensed Consolidated Statements of Operations.
(d)Defined benefit pension amounts reclassified from AOCL to expense (income) were included in Other expense, net in the Condensed Consolidated Statements of Operations.
(e)Foreign currency amounts reclassified from AOCL to expense (income) were included in Loss on sale of business, net in the Condensed Consolidated Statements of Operations. See Note 3. Dispositions for further information.
v3.26.1
DERIVATIVE FINANCIAL INSTRUMENTS
 6 Months Ended
Mar. 31, 2026
Derivative Instruments and Hedging Activities Disclosure [Abstract]  
DERIVATIVE FINANCIAL INSTRUMENTS DERIVATIVE FINANCIAL INSTRUMENTS
 
The Company is subject to various types of market risks, including interest rate risk, foreign currency exchange rate transaction and translation risk and commodity pricing risk. Management may take actions to mitigate the exposure to these types of risks, including entering into forward purchase contracts and other financial instruments. The Company manages a portion of its commodity pricing risks and foreign currency exchange rate risks by using derivative instruments. From time to time, the Company may enter into foreign exchange contracts to mitigate foreign exchange risk. The Company does not seek to engage in trading activities or take speculative positions with any financial instrument arrangement. The Company enters into natural gas derivative instruments and foreign currency derivative instruments with counterparties it views as creditworthy. However, the Company does attempt to mitigate its counterparty credit risk exposures by, among other things, entering into master netting agreements with some of these counterparties. The Company records derivative financial instruments as either assets or liabilities at fair value in its Condensed Consolidated Balance Sheets and the balances were not material as of March 31, 2026 and September 30, 2025.

Derivatives qualify for treatment as hedges when there is a high correlation between the change in fair value of the derivative instrument and the related change in value of the underlying hedged item. Depending on the exposure being hedged, the Company must designate the hedging instrument as a fair value hedge, a cash flow hedge or a net investment in foreign operations hedge. For the qualifying derivative instruments that have been designated as cash flow hedges, the effective portion of the change in fair value is recognized through earnings when the underlying transaction being hedged affects earnings, allowing a derivative’s gains and losses to offset related results from the hedged item in the Condensed Consolidated Statements of Operations. Any ineffectiveness related to these instruments accounted for as hedges was not material for any of the periods presented. For derivative instruments that have not been designated as hedges, the entire change in fair value is recorded through earnings in the period of change.

Natural Gas Derivative Instruments

Natural gas is consumed at several of the Company’s production facilities, and changes in natural gas prices impact the Company’s operating margin. The Company seeks to reduce the earnings and cash flow impacts of changes in market prices of natural gas by fixing the purchase price of up to 90% of its forecasted natural gas usage. It is the Company’s policy to consider hedging portions of its natural gas usage up to 36 months in advance of the forecasted purchase. As of March 31, 2026, the Company had entered into natural gas derivative instruments to hedge a portion of its natural gas purchase requirements through December 31, 2027. As of March 31, 2026 and September 30, 2025, the Company had agreements in place to hedge forecasted natural gas purchases of 2.5 million and 2.6 million MMBtus, respectively. All natural gas derivative instruments
held by the Company as of March 31, 2026 and September 30, 2025 qualified and were designated as cash flow hedges. The Company recorded a net expense related to the natural gas cash flow hedges of $0.0 million and $0.4 million, in Product costs, during the three months ended March 31, 2026 and March 31, 2025, respectively, and $0.5 million and $1.0 million, during the six months ended March 31, 2026 and March 31, 2025, respectively. As of March 31, 2026, the Company expects to reclassify $1.8 million of net losses on natural gas derivative instruments from AOCL to earnings during the next twelve months. Refer to Note 12. Fair Value Measurements for the estimated fair value of the Company’s natural gas derivative instruments as of March 31, 2026 and Note 10. Stockholders’ Equity and Equity Instruments for the activity related to AOCL.

The following tables present the fair value of the Company’s derivatives (in millions):
 Asset DerivativesLiability Derivatives
Consolidated Balance Sheet LocationMarch 31, 2026Consolidated Balance Sheet LocationMarch 31, 2026
Derivatives designated as hedging instruments:
Commodity contractsOther current assets$4.3 Accrued expenses and other current liabilities$6.1 
Commodity contractsOther assets1.5 Other noncurrent liabilities1.7 
Total derivatives(a)
$5.8 $7.8 
(a)The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $4.3 million of its commodity contracts that are in current receivable positions against its contracts in current payable positions and $1.5 million in long-term other asset positions against its contracts in other noncurrent liabilities positions.

 Asset DerivativesLiability Derivatives
Consolidated Balance Sheet LocationSeptember 30, 2025Consolidated Balance Sheet LocationSeptember 30, 2025
Derivatives designated as hedging instruments:
Commodity contractsOther current assets$6.2 Accrued expenses and other current liabilities$7.1 
Commodity contractsOther assets1.7 Other noncurrent liabilities1.6 
Total derivatives(a)
$7.9 $8.7 
(a)The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Condensed Consolidated Balance Sheets $7.8 million of its commodity contracts that are in receivable positions against its contracts in payable positions.
v3.26.1
FAIR VALUE MEASUREMENTS
 6 Months Ended
Mar. 31, 2026
Fair Value Disclosures [Abstract]  
FAIR VALUE MEASUREMENTS FAIR VALUE MEASUREMENTS
The Company’s financial instruments are measured and reported at their estimated fair values. Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction. When available, the Company uses quoted prices in active markets to determine the fair values for its financial instruments (Level 1 inputs) or, absent quoted market prices, observable market-corroborated inputs over the term of the financial instruments (Level 2 inputs). The Company does not have any unobservable inputs that are not corroborated by market inputs (Level 3 inputs).
 
Recurring Fair Value Measurements

The following tables summarizes the fair value hierarchy for each type of instrument carried at fair value on a recurring basis (in millions):
Fair Value Measurements at March 31, 2026 Using
 
Total Carrying Value at
March 31, 2026
Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
Asset Class:
Mutual fund investments in a non-qualified savings plan(a)(b)
$3.6 $3.6 $— $— 
Derivatives – natural gas instruments, net5.8 — 5.8 — 
Total assets at fair value$9.4 $3.6 $5.8 $— 
Liability Class:    
Derivatives - natural gas instruments, net$7.8 $— $7.8 $— 
Liabilities related to non-qualified savings plan3.6 3.6 — — 
Total liabilities at fair value$11.4 $3.6 $7.8 $— 
(a)Includes mutual fund investments of approximately 34% in common stock of large-cap U.S. companies, 4% in common stock of small to mid-cap U.S. companies, 2% in the common stock of international companies, 9% in bond funds, 16% in short-term investments, and 35% in blended funds.
(b)The investments related to a non-qualified deferred compensation arrangement on behalf of certain members of management. The Company has a liability for the related-party transaction recorded on Other noncurrent liabilities for deferred compensation obligation.
    
Fair Value Measurements at September 30, 2025 Using
 Total Carrying Value at
September 30, 2025		Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
Asset Class:
Mutual fund investments in a non-qualified savings plan(a)(b)
$3.5 $3.5 $— $— 
Derivatives – natural gas instruments, net7.9 — 7.9 — 
Total assets at fair value$11.4 $3.5 $7.9 $— 
Liability Class:    
Derivatives - natural gas instruments, net$8.7 $— $8.7 $— 
Liabilities related to non-qualified savings plan3.5 3.5 — — 
Total liabilities at fair value$12.2 $3.5 $8.7 $— 
(a)Includes mutual fund investments of approximately 29% in common stock of large-cap U.S. companies, 4% in common stock of small to mid-cap U.S. companies, 2% in the common stock of international companies, 9% in bond funds, 20% in short-term investments, and 36% in blended funds.
(b)The investments related to a non-qualified deferred compensation arrangement on behalf of certain members of management. The Company has a liability for the related-party transaction recorded on Other noncurrent liabilities for deferred compensation obligation.

Valuation Techniques: The Company holds marketable securities associated with its deferred contribution and pre-tax savings plans, which are valued based on readily available quoted market prices. The Company utilizes derivative instruments to manage its risk of changes in natural gas prices and foreign exchange rates (see Note 11. Derivative Financial Instruments). The fair values of the natural gas and foreign currency derivative instruments are determined using market data of forward prices for all of the Company’s contracts. 
Other Fair Value Measurements

The Company is required to disclose the fair value of financial instruments that are not recognized at fair value in the statement of financial position for which it is practicable to estimate that value (in millions):

Fair Value Measurements at March 31, 2026 Using
 
Total Carrying Value at
March 31, 2026
Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
8.00% Senior Notes due July 2030
$650.0 $— $671.9 $— 

Fair Value Measurements at September 30, 2025 Using
 Total Carrying Value at
September 30, 2025		Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
8.00% Senior Notes due July 2030
$650.0 $— $680.1 $— 
6.75% Senior Notes due December 2027
150.0 — 150.1 — 
Valuation Techniques: Observable market-based inputs were used to estimate fair value for Level 2 inputs, based on available trading information. Cash and cash equivalents, receivables (net of allowance for doubtful accounts) and accounts payable are carried at cost, which approximates fair value due to their liquid and short-term nature.
v3.26.1
SUPPLEMENTAL BALANCE SHEET INFORMATION
 6 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]  
SUPPLEMENTAL BALANCE SHEET INFORMATION SUPPLEMENTAL BALANCE SHEET INFORMATION
Other assets consisted of the following (in millions):
 March 31,
2026		September 30,
2025
Other current assets
Prepaid taxes$19.1 $9.7 
Other12.9 11.2 
Total other current assets$32.0 $20.9 
Other noncurrent assets
Operating lease right-of-use assets, net$48.8 $52.3 
Raw materials and supplies, net of allowance32.9 33.0 
Deposits(a)
2.8 43.8 
Other14.1 18.2 
Total other noncurrent assets$98.6 $147.3 
(a)    Refer to Note 6. Income Taxes for further information.
Other liabilities consisted of the following (in millions):
 March 31,
2026		September 30,
2025
Accrued expenses and other current liabilities
Accrued expenses$39.9 $36.5 
Legal and environmental liabilities45.6 51.8 
Current portion of operating lease liabilities15.8 14.7 
Other taxes payable6.0 7.7 
Total accrued expenses and other current liabilities$107.3 $110.7 
Other noncurrent liabilities
Noncurrent portion of operating lease liabilities$34.3 $39.2 
Tax contingencies(a)
15.5 67.4 
Other23.7 19.4 
Total other noncurrent liabilities$73.5 $126.0 
(a)    Refer to Note 6. Income Taxes for further information.
v3.26.1
NET INCOME (LOSS) PER SHARE
 6 Months Ended
Mar. 31, 2026
Earnings Per Share [Abstract]  
NET INCOME (LOSS) PER SHARE NET INCOME (LOSS) PER SHARE
 
Basic net income (loss) per share is computed by dividing net income (loss) available to common stockholders by the weighted-average number of outstanding common shares during the period. Diluted net income per share reflects the potential dilution that could occur under the more dilutive of either the treasury stock method or the two-class method for calculating the weighted-average number of outstanding common shares. Under the treasury stock method, potential shares of common shares outstanding are not included in the computation of diluted net income (loss) per share if their effect is anti-dilutive.

The following table sets forth the computation of basic and diluted net income (loss) per common share (in millions, except for share and per-share data):
 Three Months Ended
March 31,		Six Months Ended
March 31,
 2026202520262025
Numerator:
Net income (loss)$12.7 $(32.0)$31.3 $(55.6)
Less: net income allocated to participating securities(a)
(0.2)— (0.6)— 
Net income (loss) available to common stockholders$12.5 $(32.0)$30.7 $(55.6)
Denominator (in thousands):
Weighted-average common shares outstanding for basic net income (loss) per share42,160 41,521 42,105 41,480 
Weighted-average effect of dilutive equity awards outstanding197 — 192 — 
Shares for diluted net income (loss) per share(b)
42,357 41,521 42,297 41,480 
Basic net income (loss) per common share$0.30 $(0.77)$0.73 $(1.34)
Diluted net income (loss) per common share$0.30 $(0.77)$0.73 $(1.34)
(a)Weighted participating securities, consisting of RSUs that are entitled to non-forfeitable dividends if declared, totaled 889,000 and 792,000 for the three and six months ended March 31, 2026, respectively.
(b)Weighted-average equity awards outstanding of 869,000 and 1,298,000, for the three months ended March 31, 2026 and March 31, 2025, respectively, and 770,000 and 1,227,000, for the six months ended March 31, 2026 and March 31, 2025, respectively, were excluded from diluted net income (loss) per common share as they were anti-dilutive.
v3.26.1
RELATED PARTY TRANSACTIONS
 6 Months Ended
Mar. 31, 2026
Related Party Transactions [Abstract]  
RELATED PARTY TRANSACTIONS RELATED PARTY TRANSACTIONS
The Company recorded SOP sales to certain subsidiaries of Koch Industries, Inc., which are considered related parties, of approximately $0.4 million and $0.8 million, for the three months ended March 31, 2026 and March 31, 2025, respectively, and $0.9 million and $1.9 million for the six months ended March 31, 2026 and March 31, 2025, respectively. As of March 31, 2026 and September 30, 2025, the Company recorded $0.0 million and $0.2 million, respectively, of receivables due from Koch Industries, Inc. in its Condensed Consolidated Balance Sheets. The Company had no related-party payables outstanding due to Koch Industries, Inc. as of March 31, 2026 and September 30, 2025.

Effective December 18, 2025, a new member was appointed to the Company’s board of directors. The new director also serves as President and Chief Executive Officer of another company from which the Company purchased approximately $1.1 million and $2.2 million of salt-treatment materials during the three and six months ended March 31, 2026, respectively, constituting a related party transaction. In addition, the Company has a payable of approximately $0.1 million outstanding as of March 31, 2026, related to this transaction.
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
ACCOUNTING POLICIES AND BASIS OF PRESENTATION (Policies)
 6 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]  
Basis of Consolidation
CMI is a holding company with no significant operations other than those of its wholly-owned subsidiaries. The consolidated financial statements include the accounts of CMI and its wholly-owned domestic and foreign subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.
Basis of Presentation
The accompanying condensed consolidated balance sheet as of September 30, 2025, which was derived from audited financial statements, and the unaudited condensed consolidated financial statements (“Condensed Consolidated Financial Statements”) have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete consolidated financial statements. As a result, these Condensed Consolidated Financial Statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended September 30, 2025. In the opinion of management, these interim financial statements reflect all adjustments, consisting of normal recurring adjustments considered necessary for a fair presentation of the Company’s financial position and results of operations.
Accounting Pronouncements Issued Not Yet Adopted
Accounting Pronouncements Issued Not Yet Adopted

Income Tax Disclosures. In December 2023, the Financial Accounting Standards Board (“FASB”) issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which updates income tax disclosures by requiring consistent categories and additional disaggregation of information in the rate reconciliation and income taxes paid by jurisdiction. The ASU is effective for fiscal years beginning after December 15, 2024, and is effective for the Company beginning in the annual report for the fiscal year ended September 30, 2026. Early adoption is permitted. The amendments should be applied prospectively; however, retrospective application is permitted. Management is currently evaluating this ASU to determine its impact on the Company’s disclosures.

Disaggregation of Income Statement Expenses. In November 2024, the FASB issued amended guidance related to disclosure of disaggregated expenses (“ASU 2024-03”). This amendment requires public business entities to provide detailed disclosures in the notes to financial statements disaggregating specific expense categories, including purchases of inventory, employee compensation, depreciation, depletion, and intangible asset amortization, as well as certain other disclosures to provide enhanced transparency into the nature and function of expenses. This guidance is effective for annual periods beginning with the Company’s annual report for the fiscal year ended September 30, 2028, and interim periods following annual adoption, with early adoption permitted. This guidance will be applied on a prospective basis with retrospective application permitted. Management is currently evaluating ASU 2024-03 to determine its impact on the Company’s disclosures.

Interim Reporting. In December 2025, the FASB issued ASU 2025-11, Interim Reporting (Topic 270): Narrow-Scope Improvements (“ASU 2025-11”), to improve the guidance for interim reporting and clarify when that guidance is applicable. This ASU provides a comprehensive list of required interim disclosures and also requires entities to disclose events since the end of the last annual reporting period that have a material impact on the entity. ASU 2025-11 is effective for interim reporting periods within annual reporting periods beginning after December 15, 2027. For the Company, the guidance becomes effective in the first interim period of the fiscal year ended September 30, 2029. Early adoption is permitted. Management is currently evaluating ASU 2025-11 to determine its impact on the Company’s disclosures.
Deferred Revenue
Deferred Revenue
Deferred revenue represents collections under contracts before the related product or service is transferred to the customer. The portion of deferred revenue that is anticipated to be recognized as revenue during the succeeding twelve-month period is recorded in Accrued expenses and other current liabilities in the Condensed Consolidated Balance Sheets.
Derivative Financial Instruments
The Company is subject to various types of market risks, including interest rate risk, foreign currency exchange rate transaction and translation risk and commodity pricing risk. Management may take actions to mitigate the exposure to these types of risks, including entering into forward purchase contracts and other financial instruments. The Company manages a portion of its commodity pricing risks and foreign currency exchange rate risks by using derivative instruments. From time to time, the Company may enter into foreign exchange contracts to mitigate foreign exchange risk. The Company does not seek to engage in trading activities or take speculative positions with any financial instrument arrangement. The Company enters into natural gas derivative instruments and foreign currency derivative instruments with counterparties it views as creditworthy. However, the Company does attempt to mitigate its counterparty credit risk exposures by, among other things, entering into master netting agreements with some of these counterparties. The Company records derivative financial instruments as either assets or liabilities at fair value in its Condensed Consolidated Balance Sheets and the balances were not material as of March 31, 2026 and September 30, 2025.
Derivatives qualify for treatment as hedges when there is a high correlation between the change in fair value of the derivative instrument and the related change in value of the underlying hedged item. Depending on the exposure being hedged, the Company must designate the hedging instrument as a fair value hedge, a cash flow hedge or a net investment in foreign operations hedge. For the qualifying derivative instruments that have been designated as cash flow hedges, the effective portion of the change in fair value is recognized through earnings when the underlying transaction being hedged affects earnings, allowing a derivative’s gains and losses to offset related results from the hedged item in the Condensed Consolidated Statements of Operations. Any ineffectiveness related to these instruments accounted for as hedges was not material for any of the periods presented. For derivative instruments that have not been designated as hedges, the entire change in fair value is recorded through earnings in the period of change.
v3.26.1
REVENUES (Tables)
 6 Months Ended
Mar. 31, 2026
Revenue from Contract with Customer [Abstract]  
Schedule of Disaggregation of Revenue
Sales is disaggregated in the following table by timing of revenue recognition (in millions):
 Three Months Ended
March 31,		Six Months Ended
March 31,
 2026202520262025
Timing of revenue recognition:
Products and services transferred at a point in time$450.4 $492.0 $843.7 $796.6 
Products and services transferred over time(a)
2.8 2.6 5.6 5.2 
Total sales$453.2 $494.6 $849.3 $801.8 
(a)     Amounts include records management business utilizing excavated areas of its Winsford salt mine with one other location in London, England.
Disaggregated revenue by product type is as follows (in millions):
Three Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$278.9 $— $— $278.9 
Consumer & Industrial Salt103.7 — — 103.7 
SOP— 69.0 — 69.0 
Eliminations & Other— (2.0)3.6 1.6 
Sales to external customers$382.6 $67.0 $3.6 $453.2 
Three Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$324.8 $— $— $324.8 
Consumer & Industrial Salt107.9 — — 107.9 
SOP— 60.6 — 60.6 
Eliminations & Other— (2.3)3.6 1.3 
Sales to external customers$432.7 $58.3 $3.6 $494.6 

Six Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$489.7 $— $— $489.7 
Consumer & Industrial Salt224.4— — 224.4 
SOP— 130.8 — 130.8 
Eliminations & Other— (3.0)7.4 4.4 
Sales to external customers$714.1 $127.8 $7.4 $849.3 

Six Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$462.9 $— $— $462.9 
Consumer & Industrial Salt212.0 — — 212.0 
SOP— 125.2 — 125.2 
Eliminations & Other— (5.5)7.2 1.7 
Sales to external customers$674.9 $119.7 $7.2 $801.8 
(a)Corporate and Other includes corporate entities, records management operations and other incidental operations and eliminations. Operating income (loss) for Corporate and Other includes indirect corporate overhead, including costs for general corporate governance and oversight, as well as costs for human resources, information technology, legal and finance functions.
(b)Sales to external customers are net of intersegment sales.
(c)The Company recorded a pre-tax Loss on sale of business, net, of $14.6 million, which included $13.1 million of cumulative foreign currency translation adjustments reclassified from Accumulated other comprehensive loss, for both the three and six months ended March 31, 2026.
(d)The Company recorded an impairment loss of $53.0 million related to the exit of the Fortress fire retardant business for both the three and six months ended March 31, 2025.
(e)For the three and six months ended March 31, 2025, the Company recorded costs of $0.9 million and $1.8 million, respectively, related to a recall of food-grade salt produced at its Goderich plant.
(f)For the three and six months ended March 31, 2025, the Company incurred severance and related charges of $4.0 million, due to a reduction in workforce, changes to executive leadership and additional restructuring costs related to the exit of the Fortress fire retardant business.
Schedule of Balances of Receivables
The following table provides the balances of receivables (in millions):
 March 31,
2026		September 30,
2025
Current assets:
Receivables related to contracts with customers
$170.4 $127.3 
Miscellaneous receivables(a)
52.9 52.3 
Total receivables
$223.3 $179.6 
(a)Refer to Note 8. Commitments and Contingencies for additional information.
v3.26.1
INVENTORIES (Tables)
 6 Months Ended
Mar. 31, 2026
Inventory Disclosure [Abstract]  
Schedule of Inventories
Inventories consist of the following (in millions):
 March 31,
2026		September 30,
2025
Finished goods$76.5 $219.1 
Work in process5.9 5.9 
Raw materials and supplies(a)
96.3 87.0 
Total inventories$178.7 $312.0 
(a)Excludes certain raw materials and supplies of $32.9 million and $33.0 million as of March 31, 2026 and September 30, 2025, respectively, that are not expected to be consumed within the next twelve months, included in Other noncurrent assets in the Condensed Consolidated Balance Sheets.
v3.26.1
PROPERTY, PLANT AND EQUIPMENT, NET (Tables)
 6 Months Ended
Mar. 31, 2026
Property, Plant and Equipment [Abstract]  
Schedule of Property, Plant and Equipment, Net
Property, plant and equipment, net, consists of the following (in millions):
 March 31,
2026		September 30,
2025
Land, buildings and structures, and leasehold improvements(a)
$543.3 $554.1 
Machinery and equipment(a)
1,156.7 1,154.9 
Office furniture and equipment23.4 23.9 
Mineral interests168.6 169.1 
Construction in progress56.7 51.6 
 1,948.7 1,953.6 
Less: accumulated depreciation, depletion, and amortization(1,200.4)(1,183.5)
Property, plant and equipment, net$748.3 $770.1 
(a)    Includes finance lease right-of-use assets.
Schedule of Supplemental Non-cash Activities
The following table provides supplemental non-cash activities (in million):
Six Months Ended
March 31,
 20262025
Purchases of Property, plant and equipment in Accounts payable$8.6 $6.2 
Purchases of Property, plant and equipment in Accrued expenses and other current liabilities3.8 5.1 
Transfers of Property, plant and equipment from Inventory6.1 3.7 
v3.26.1
LONG-TERM DEBT AND FINANCE LEASE LIABILITIES (Tables)
 6 Months Ended
Mar. 31, 2026
Debt Disclosure [Abstract]  
Schedule of Total Long-Term Carrying Value of Debt and Finance Lease Liabilities
Total long-term carrying value of debt and finance lease liabilities consists of the following (in millions):
 March 31,
2026		September 30,
2025
Secured Debt:
Revolving Credit Facility due May 2028$— $— 
Subordinated Debt:
8.00% Senior Notes due July 2030
650.0 650.0 
6.75% Senior Notes due December 2027
— 150.0 
Accounts Receivable Securitization Facility75.0 45.8 
Total principal amount of debt725.0 845.8 
Finance lease liabilities12.3 15.5 
Unamortized deferred financing costs(12.0)(13.6)
Total carrying value of debt and finance lease liabilities725.3 847.7 
Current portion of finance lease liabilities(6.4)(7.9)
Total long-term carrying value of debt and finance lease liabilities$718.9 $839.8 
v3.26.1
OPERATING SEGMENTS (Tables)
 6 Months Ended
Mar. 31, 2026
Segment Reporting [Abstract]  
Schedule of Segment Information
Segment information is as follows (in millions):
Three Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Sales to external customers(b)
$382.6 $67.0 $3.6 $453.2 
Intersegment sales— 2.0 (2.0)— 
Shipping and handling cost128.7 9.3 — 138.0 
Product cost181.1 48.7 2.4 232.2 
Gross profit72.8 9.0 1.2 83.0 
Selling, general and administrative expenses7.6 1.4 18.0 27.0 
Operating income (loss)65.2 7.6 (16.8)56.0 
Other Segment Disclosures:
Depreciation, depletion and amortization18.0 9.3 0.9 28.2 
Loss on sale of business, net(d)
— 14.6 — 14.6 
Total assets (as of end of period)825.3 338.2 201.8 1,365.3 

Three Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Sales to external customers(b)
$432.7 $58.3 $3.6 $494.6 
Intersegment sales— 2.3 (2.3)— 
Shipping and handling cost141.9 9.5 — 151.4 
Product cost214.3 48.6 3.5 266.4 
Gross profit76.5 0.2 0.1 76.8 
Selling, general and administrative expenses9.1 2.0 18.5 29.6 
Loss on impairments(c)
— — 53.0 53.0 
Other operating expense (income)0.5 — (3.2)(2.7)
Operating income (loss)66.9 (1.8)(68.2)(3.1)
Other Segment Disclosures:
Depreciation, depletion and amortization17.4 7.4 1.7 26.5 
Total assets (as of end of period)959.2 365.7 207.0 1,531.9 
Six Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Sales to external customers(b)
$714.1 $127.8 $7.4 $849.3 
Intersegment sales— 3.0 (3.0)— 
Shipping and handling cost232.5 17.6 — 250.1 
Product cost353.1 95.0 4.9 453.0 
Gross profit128.5 15.2 2.5 146.2 
Selling, general and administrative expenses14.2 2.2 37.2 53.6 
Operating income (loss)114.3 13.0 (34.7)92.6 
Other Segment Disclosures:
Depreciation, depletion and amortization36.1 16.7 1.8 54.6 
Loss on sale of business, net(d)
— 14.6 — 14.6 
Capital expenditures31.0 9.2 0.8 41.0 

Six Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Sales to external customers(b)
$674.9 $119.7 $7.2 $801.8 
Intersegment sales— 5.5 (5.5)— 
Shipping and handling cost213.2 18.8 — 232.0 
Product cost348.4 103.0 7.3 458.7 
Gross profit (loss)113.3 (2.1)(0.1)111.1 
Selling, general and administrative expenses16.5 2.8 43.6 62.9 
Loss on impairments(c)
— — 53.0 53.0 
Other operating expense (income)0.5 — (2.7)(2.2)
Operating income (loss)96.3 (4.9)(94.0)(2.6)
Other Segment Disclosures:
Depreciation, depletion and amortization34.9 14.9 3.5 53.3 
Capital expenditures27.5 6.2 2.1 35.8 
Schedule of Disaggregated Revenue by Product Type
Sales is disaggregated in the following table by timing of revenue recognition (in millions):
 Three Months Ended
March 31,		Six Months Ended
March 31,
 2026202520262025
Timing of revenue recognition:
Products and services transferred at a point in time$450.4 $492.0 $843.7 $796.6 
Products and services transferred over time(a)
2.8 2.6 5.6 5.2 
Total sales$453.2 $494.6 $849.3 $801.8 
(a)     Amounts include records management business utilizing excavated areas of its Winsford salt mine with one other location in London, England.
Disaggregated revenue by product type is as follows (in millions):
Three Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$278.9 $— $— $278.9 
Consumer & Industrial Salt103.7 — — 103.7 
SOP— 69.0 — 69.0 
Eliminations & Other— (2.0)3.6 1.6 
Sales to external customers$382.6 $67.0 $3.6 $453.2 
Three Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$324.8 $— $— $324.8 
Consumer & Industrial Salt107.9 — — 107.9 
SOP— 60.6 — 60.6 
Eliminations & Other— (2.3)3.6 1.3 
Sales to external customers$432.7 $58.3 $3.6 $494.6 

Six Months Ended March 31, 2026SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$489.7 $— $— $489.7 
Consumer & Industrial Salt224.4— — 224.4 
SOP— 130.8 — 130.8 
Eliminations & Other— (3.0)7.4 4.4 
Sales to external customers$714.1 $127.8 $7.4 $849.3 

Six Months Ended March 31, 2025SaltPlant
Nutrition
Corporate
& Other(a)
Total
Highway Deicing Salt$462.9 $— $— $462.9 
Consumer & Industrial Salt212.0 — — 212.0 
SOP— 125.2 — 125.2 
Eliminations & Other— (5.5)7.2 1.7 
Sales to external customers$674.9 $119.7 $7.2 $801.8 
(a)Corporate and Other includes corporate entities, records management operations and other incidental operations and eliminations. Operating income (loss) for Corporate and Other includes indirect corporate overhead, including costs for general corporate governance and oversight, as well as costs for human resources, information technology, legal and finance functions.
(b)Sales to external customers are net of intersegment sales.
(c)The Company recorded a pre-tax Loss on sale of business, net, of $14.6 million, which included $13.1 million of cumulative foreign currency translation adjustments reclassified from Accumulated other comprehensive loss, for both the three and six months ended March 31, 2026.
(d)The Company recorded an impairment loss of $53.0 million related to the exit of the Fortress fire retardant business for both the three and six months ended March 31, 2025.
(e)For the three and six months ended March 31, 2025, the Company recorded costs of $0.9 million and $1.8 million, respectively, related to a recall of food-grade salt produced at its Goderich plant.
(f)For the three and six months ended March 31, 2025, the Company incurred severance and related charges of $4.0 million, due to a reduction in workforce, changes to executive leadership and additional restructuring costs related to the exit of the Fortress fire retardant business.
v3.26.1
STOCKHOLDERS’ EQUITY AND EQUITY INSTRUMENTS (Tables)
 6 Months Ended
Mar. 31, 2026
Equity [Abstract]  
Schedule of Stock-Based Compensation Activity
The following table summarizes stock-based compensation activity during the six months ended March 31, 2026:
 Stock OptionsRSUs
PSUs(a)
 NumberWeighted-average
exercise price		NumberWeighted-average
fair value		NumberWeighted-average
fair value
Outstanding at September 30, 2025
107,261 $63.43 828,922 $15.34 316,480 $16.89 
Granted— — 478,287 18.47 182,071 19.37 
Released from restriction(b)
— — (318,033)15.69 — — 
Cancelled/expired(794)67.50 (15,573)24.43 — — 
Outstanding at March 31, 2026
106,467 $63.40 973,603 $16.63 498,551 $17.80 
(a)Until the performance period is completed, PSUs are included in the table at the target level at their grant date and at that target level represents one share of common stock per PSU.
(b)The Company paid taxes for restricted unit withholdings of approximately $1.7 million during the six months ended March 31, 2026.
Schedule of Components and Changes in Accumulated Other Comprehensive Income (Loss)
The following table presents the change in AOCL by component (in millions):

Six Months Ended March 31, 2026(a)
Gains and (Losses) on Cash Flow HedgesDefined Benefit PensionOther Post-Employment BenefitsForeign CurrencyTotal
Beginning balance$(0.8)$(6.3)$1.8 $(102.6)$(107.9)
Other comprehensive loss before reclassifications(b)
(1.7)— — (6.2)(7.9)
Amounts reclassified from AOCL(c)(d)(e)
0.5 0.4 — 13.1 14.0 
Net current period other comprehensive income (loss)(1.2)0.4 — 6.9 6.1 
Ending balance$(2.0)$(5.9)$1.8 $(95.7)$(101.8)
(a)With the exception of the CTA and cash flow hedges, for which no tax effect is recorded, the changes in the components of AOCL presented in the tables above are reflected net of applicable income taxes.
(b)The Company recorded foreign exchange gain of $0.2 million in the six months ended March 31, 2026, in AOCL related to intercompany notes which were deemed to be of a long-term investment nature.
(c)Cash flow hedge amounts reclassified from AOCL to expense (income) were included in Product cost in the Condensed Consolidated Statements of Operations.
(d)Defined benefit pension amounts reclassified from AOCL to expense (income) were included in Other expense, net in the Condensed Consolidated Statements of Operations.
(e)Foreign currency amounts reclassified from AOCL to expense (income) were included in Loss on sale of business, net in the Condensed Consolidated Statements of Operations. See Note 3. Dispositions for further information.
v3.26.1
DERIVATIVE FINANCIAL INSTRUMENTS (Tables)
 6 Months Ended
Mar. 31, 2026
Derivative Instruments and Hedging Activities Disclosure [Abstract]  
Schedule of Fair Value of Derivatives
The following tables present the fair value of the Company’s derivatives (in millions):
 Asset DerivativesLiability Derivatives
Consolidated Balance Sheet LocationMarch 31, 2026Consolidated Balance Sheet LocationMarch 31, 2026
Derivatives designated as hedging instruments:
Commodity contractsOther current assets$4.3 Accrued expenses and other current liabilities$6.1 
Commodity contractsOther assets1.5 Other noncurrent liabilities1.7 
Total derivatives(a)
$5.8 $7.8 
(a)The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Consolidated Balance Sheets $4.3 million of its commodity contracts that are in current receivable positions against its contracts in current payable positions and $1.5 million in long-term other asset positions against its contracts in other noncurrent liabilities positions.

 Asset DerivativesLiability Derivatives
Consolidated Balance Sheet LocationSeptember 30, 2025Consolidated Balance Sheet LocationSeptember 30, 2025
Derivatives designated as hedging instruments:
Commodity contractsOther current assets$6.2 Accrued expenses and other current liabilities$7.1 
Commodity contractsOther assets1.7 Other noncurrent liabilities1.6 
Total derivatives(a)
$7.9 $8.7 
(a)The Company has master netting agreements with its commodity hedge counterparties and accordingly has netted in its Condensed Consolidated Balance Sheets $7.8 million of its commodity contracts that are in receivable positions against its contracts in payable positions.
v3.26.1
FAIR VALUE MEASUREMENTS (Tables)
 6 Months Ended
Mar. 31, 2026
Fair Value Disclosures [Abstract]  
Schedule of Estimated Fair Values for Type of Instrument
The following tables summarizes the fair value hierarchy for each type of instrument carried at fair value on a recurring basis (in millions):
Fair Value Measurements at March 31, 2026 Using
 
Total Carrying Value at
March 31, 2026
Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
Asset Class:
Mutual fund investments in a non-qualified savings plan(a)(b)
$3.6 $3.6 $— $— 
Derivatives – natural gas instruments, net5.8 — 5.8 — 
Total assets at fair value$9.4 $3.6 $5.8 $— 
Liability Class:    
Derivatives - natural gas instruments, net$7.8 $— $7.8 $— 
Liabilities related to non-qualified savings plan3.6 3.6 — — 
Total liabilities at fair value$11.4 $3.6 $7.8 $— 
(a)Includes mutual fund investments of approximately 34% in common stock of large-cap U.S. companies, 4% in common stock of small to mid-cap U.S. companies, 2% in the common stock of international companies, 9% in bond funds, 16% in short-term investments, and 35% in blended funds.
(b)The investments related to a non-qualified deferred compensation arrangement on behalf of certain members of management. The Company has a liability for the related-party transaction recorded on Other noncurrent liabilities for deferred compensation obligation.
    
Fair Value Measurements at September 30, 2025 Using
 Total Carrying Value at
September 30, 2025		Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
Asset Class:
Mutual fund investments in a non-qualified savings plan(a)(b)
$3.5 $3.5 $— $— 
Derivatives – natural gas instruments, net7.9 — 7.9 — 
Total assets at fair value$11.4 $3.5 $7.9 $— 
Liability Class:    
Derivatives - natural gas instruments, net$8.7 $— $8.7 $— 
Liabilities related to non-qualified savings plan3.5 3.5 — — 
Total liabilities at fair value$12.2 $3.5 $8.7 $— 
(a)Includes mutual fund investments of approximately 29% in common stock of large-cap U.S. companies, 4% in common stock of small to mid-cap U.S. companies, 2% in the common stock of international companies, 9% in bond funds, 20% in short-term investments, and 36% in blended funds.
(b)The investments related to a non-qualified deferred compensation arrangement on behalf of certain members of management. The Company has a liability for the related-party transaction recorded on Other noncurrent liabilities for deferred compensation obligation.
The Company is required to disclose the fair value of financial instruments that are not recognized at fair value in the statement of financial position for which it is practicable to estimate that value (in millions):

Fair Value Measurements at March 31, 2026 Using
 
Total Carrying Value at
March 31, 2026
Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
8.00% Senior Notes due July 2030
$650.0 $— $671.9 $— 

Fair Value Measurements at September 30, 2025 Using
 Total Carrying Value at
September 30, 2025		Quoted Prices in Active Market
(Level One)		Significant Other Observable Inputs
(Level Two)		Significant Unobservable Inputs
(Level Three)
8.00% Senior Notes due July 2030
$650.0 $— $680.1 $— 
6.75% Senior Notes due December 2027
150.0 — 150.1 — 
v3.26.1
SUPPLEMENTAL BALANCE SHEET INFORMATION (Tables)
 6 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]  
Schedule of Other Current Assets
Other assets consisted of the following (in millions):
 March 31,
2026		September 30,
2025
Other current assets
Prepaid taxes$19.1 $9.7 
Other12.9 11.2 
Total other current assets$32.0 $20.9 
Other noncurrent assets
Operating lease right-of-use assets, net$48.8 $52.3 
Raw materials and supplies, net of allowance32.9 33.0 
Deposits(a)
2.8 43.8 
Other14.1 18.2 
Total other noncurrent assets$98.6 $147.3 
(a)    Refer to Note 6. Income Taxes for further information.
Schedule of Other Liabilities
Other liabilities consisted of the following (in millions):
 March 31,
2026		September 30,
2025
Accrued expenses and other current liabilities
Accrued expenses$39.9 $36.5 
Legal and environmental liabilities45.6 51.8 
Current portion of operating lease liabilities15.8 14.7 
Other taxes payable6.0 7.7 
Total accrued expenses and other current liabilities$107.3 $110.7 
Other noncurrent liabilities
Noncurrent portion of operating lease liabilities$34.3 $39.2 
Tax contingencies(a)
15.5 67.4 
Other23.7 19.4 
Total other noncurrent liabilities$73.5 $126.0 
(a)    Refer to Note 6. Income Taxes for further information.
v3.26.1
NET INCOME (LOSS) PER SHARE (Tables)
 6 Months Ended
Mar. 31, 2026
Earnings Per Share [Abstract]  
Schedule of Computation of Basic and Diluted Net Income (Loss) Per Common Share
The following table sets forth the computation of basic and diluted net income (loss) per common share (in millions, except for share and per-share data):
 Three Months Ended
March 31,		Six Months Ended
March 31,
 2026202520262025
Numerator:
Net income (loss)$12.7 $(32.0)$31.3 $(55.6)
Less: net income allocated to participating securities(a)
(0.2)— (0.6)— 
Net income (loss) available to common stockholders$12.5 $(32.0)$30.7 $(55.6)
Denominator (in thousands):
Weighted-average common shares outstanding for basic net income (loss) per share42,160 41,521 42,105 41,480 
Weighted-average effect of dilutive equity awards outstanding197 — 192 — 
Shares for diluted net income (loss) per share(b)
42,357 41,521 42,297 41,480 
Basic net income (loss) per common share$0.30 $(0.77)$0.73 $(1.34)
Diluted net income (loss) per common share$0.30 $(0.77)$0.73 $(1.34)
(a)Weighted participating securities, consisting of RSUs that are entitled to non-forfeitable dividends if declared, totaled 889,000 and 792,000 for the three and six months ended March 31, 2026, respectively.
(b)Weighted-average equity awards outstanding of 869,000 and 1,298,000, for the three months ended March 31, 2026 and March 31, 2025, respectively, and 770,000 and 1,227,000, for the six months ended March 31, 2026 and March 31, 2025, respectively, were excluded from diluted net income (loss) per common share as they were anti-dilutive.
v3.26.1
REVENUES - Schedule of Disaggregation of Revenue (Details)
$ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2026
USD ($)
business
Mar. 31, 2025
USD ($)
Mar. 31, 2026
USD ($)
business
Mar. 31, 2025
USD ($)
Disaggregation of Revenue [Line Items]        
Total sales $ 453.2 $ 494.6 $ 849.3 $ 801.8
London, England        
Disaggregation of Revenue [Line Items]        
Number of business utilizing excavated areas | business 1   1  
Products and services transferred at a point in time        
Disaggregation of Revenue [Line Items]        
Total sales $ 450.4 492.0 $ 843.7 796.6
Products and services transferred over time        
Disaggregation of Revenue [Line Items]        
Total sales $ 2.8 $ 2.6 $ 5.6 $ 5.2
v3.26.1
REVENUES - Schedule of Balances of Receivables (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Current assets:    
Receivables related to contracts with customers $ 170.4 $ 127.3
Miscellaneous receivables 52.9 52.3
Total receivables $ 223.3 $ 179.6
v3.26.1
REVENUES - Narrative (Details) - USD ($)
$ in Millions
 6 Months Ended
Mar. 31, 2026
Sep. 30, 2025
Revenue from Contract with Customer [Abstract]    
Deferred revenue $ 0.8 $ 1.6
Revenue recognized $ 0.8  
v3.26.1
DISPOSITIONS - Narrative (Details)
$ in Millions, $ in Millions
 3 Months Ended 6 Months Ended
Mar. 01, 2026
USD ($)
Feb. 02, 2026
USD ($)
May 05, 2023
USD ($)
Mar. 31, 2026
USD ($)
Mar. 31, 2025
USD ($)
Mar. 31, 2026
USD ($)
Mar. 31, 2025
USD ($)
Mar. 01, 2028
CAD ($)
Mar. 01, 2027
CAD ($)
Mar. 01, 2026
CAD ($)
Dec. 31, 2024
USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Cash proceeds           $ 23.2 $ 0.0        
Loss on sale of business, net       $ 14.6 $ 0.0 14.6 0.0        
Realized loss on foreign currency transactions reclassified into Loss on sale of business, net       (13.1) 0.0 (13.1) 0.0        
Contingent consideration, liability                     $ 7.9
Contingent consideration, liability, current                     0.1
Contingent consideration, liability, noncurrent                     $ 7.8
Net gain from remeasurement of contingent consideration           0.0 (7.9)        
Customer Relationships                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Impairment of intangible asset       52.9   52.9          
Trade Names                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Impairment of intangible asset       0.1   0.1          
Fortress                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Contingent consideration, liability     $ 28.0   0.0   0.0        
Performance period     5 years                
Contingent consideration period     10 years                
Net gain from remeasurement of contingent consideration         $ 7.9   $ 7.9        
Fortress | Significant Unobservable Inputs (Level Three) | Customer Relationships                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Definitive-lived intangible assets       0.0   0.0          
Fortress | Significant Unobservable Inputs (Level Three) | Trade Names                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Definitive-lived intangible assets       0.0   0.0          
Fortress                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Carrying value of asset to be disposed of       $ 19.7   $ 19.7          
Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOP Facility                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Gross proceeds received   $ 30.8                  
Working capital adjustments   2.1                  
Cash proceeds $ 23.2                    
Escrow deposit 3.9                 $ 5.2  
Cash on hand 1.3                    
Transaction costs 0.3                    
Loss on sale of business, net   14.6                  
Realized loss on foreign currency transactions reclassified into Loss on sale of business, net   $ 13.1                  
Net assets 30.2                    
Cash and cash equivalents 1.3                    
Intangible assets 19.1                    
Property, plant and equipment 9.0                    
Other assets and liabilities, net $ 0.8                    
Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOP Facility | Forecast                      
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                      
Escrow deposit released               $ 1.9 $ 3.3    
v3.26.1
INVENTORIES (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Inventory Disclosure [Abstract]    
Finished goods $ 76.5 $ 219.1
Work in process 5.9 5.9
Raw materials and supplies 96.3 87.0
Total inventories 178.7 312.0
Raw materials and supplies, net of allowance $ 32.9 $ 33.0
v3.26.1
PROPERTY, PLANT AND EQUIPMENT, NET - Schedule of Property, Plant and Equipment, Net (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 1,948.7 $ 1,953.6
Less: accumulated depreciation, depletion, and amortization (1,200.4) (1,183.5)
Property, plant and equipment, net 748.3 770.1
Land, buildings and structures, and leasehold improvements    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 543.3 554.1
Machinery and equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 1,156.7 1,154.9
Office furniture and equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 23.4 23.9
Mineral interests    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 168.6 169.1
Construction in progress    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 56.7 $ 51.6
v3.26.1
PROPERTY, PLANT AND EQUIPMENT, NET - Schedule of Supplemental Non-Cash Activities (Details) - USD ($)
$ in Millions
 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Property, Plant and Equipment [Abstract]    
Purchases of Property, plant and equipment in Accounts payable $ 8.6 $ 6.2
Purchases of Property, plant and equipment in Accrued expenses and other current liabilities 3.8 5.1
Transfers of Property, plant and equipment from Inventory $ 6.1 $ 3.7
v3.26.1
INCOME TAXES (Details) - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended 6 Months Ended
Dec. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Sep. 30, 2025
Income Tax Disclosure [Line Items]            
Nondeductible executive compensation       $ 1.0    
Income tax benefit   $ (16.0) $ (9.8) (13.8) $ (19.5)  
Domestic Tax Jurisdiction            
Income Tax Disclosure [Line Items]            
Additional valuation allowance   0.1   0.1    
Foreign Tax Authority            
Income Tax Disclosure [Line Items]            
Net operating loss carryforwards   80.5   80.5   $ 80.5
Remaining settlement amount $ 24.8          
Increase in other current assets       21.9    
Decrease in other noncurrent assets       47.1    
Decrease in other noncurrent liabilities       54.0    
Foreign Tax Authority | Canadian Tax Authority            
Income Tax Disclosure [Line Items]            
Total reassessments including interest           209.8
Payment for tax settlement   8.2   8.2    
Income tax benefit       4.0    
Amount of security posted in the form of cash   35.8   35.8   35.8
Amount of security posted in the form of a performance bond   157.4   157.4    
State and Local | NOL Carryforwards Expire Beginning In 2031            
Income Tax Disclosure [Line Items]            
Net operating loss carryforwards   $ 7.1   $ 7.1   $ 7.1
v3.26.1
LONG-TERM DEBT AND FINANCE LEASE LIABILITIES - Schedule of Long-Term Debt and Finance Lease Liabilities (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Jun. 16, 2025
Nov. 30, 2019
Debt Instrument [Line Items]        
Total principal amount of debt $ 725.0 $ 845.8    
Finance lease liabilities 12.3 15.5    
Unamortized deferred financing costs (12.0) (13.6)    
Total carrying value of debt and finance lease liabilities 725.3 847.7    
Current portion of finance lease liabilities (6.4) (7.9)    
Total long-term carrying value of debt and finance lease liabilities 718.9 839.8    
Line of Credit | Revolving Credit Facility due May 2028        
Debt Instrument [Line Items]        
Total principal amount of debt 0.0 0.0    
Line of Credit | Accounts Receivable Securitization Facility        
Debt Instrument [Line Items]        
Total principal amount of debt $ 75.0 $ 45.8    
Senior Notes | 0.08 Senior Notes due July 2030        
Debt Instrument [Line Items]        
Stated interest rate 8.00% 8.00% 8.00%  
Total principal amount of debt $ 650.0 $ 650.0    
Senior Notes | 6.75% Senior Notes due December 2027        
Debt Instrument [Line Items]        
Stated interest rate 6.75% 6.75%   6.75%
Total principal amount of debt $ 0.0 $ 150.0    
v3.26.1
LONG-TERM DEBT AND FINANCE LEASE LIABILITIES - Narrative (Details) - USD ($)
 3 Months Ended 6 Months Ended
Mar. 30, 2026
Jun. 17, 2025
Jun. 16, 2025
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Sep. 30, 2025
Jun. 30, 2020
Nov. 30, 2019
Debt Instrument [Line Items]                    
Loss on extinguishment of debt       $ (500,000) $ 0 $ (500,000) $ 0      
Unallocated Financing Receivables | Account Receivable Financing Receivable                    
Debt Instrument [Line Items]                    
Revolving accounts receivable financing facility                 $ 100,000,000.0  
Senior Notes | 0.08 Senior Notes due July 2030                    
Debt Instrument [Line Items]                    
Stated interest rate     8.00% 8.00%   8.00%   8.00%    
Aggregate principal amount     $ 650,000,000.0              
Debt issuance costs     $ 13,000,000.0              
Debt instrument, term     5 years              
Senior Notes | 6.75% Senior Notes due December 2027                    
Debt Instrument [Line Items]                    
Stated interest rate       6.75%   6.75%   6.75%   6.75%
Aggregate principal amount   $ 150,000,000.0               $ 500,000,000
Required prepayment of term loan $ 150,000,000.0 $ 350,000,000.0                
Accrued interest percentage 100.00%                  
Line of Credit | Amended And Restated 2023 Credit Agreement | Revolving Credit Facility                    
Debt Instrument [Line Items]                    
Aggregate principal amount of credit facility     $ 325,000,000.0              
Outstanding borrowing       $ 0   $ 0        
Availability under revolving credit facility       304,800,000   304,800,000        
Line of Credit | Amended And Restated 2023 Credit Agreement | Letter of Credit                    
Debt Instrument [Line Items]                    
Outstanding borrowing       $ 20,200,000   $ 20,200,000        
v3.26.1
COMMITMENTS AND CONTINGENCIES (Details)
$ in Millions
Jan. 07, 2026
USD ($)
Mar. 31, 2026
USD ($)
Sep. 30, 2025
USD ($)
Jun. 03, 2025
action
Feb. 01, 2023
action
Loss Contingencies [Line Items]          
Number of actions | action       2 2
Litigation settlement, amount awarded to other party $ 4.9        
Payments for legal settlements $ 1.0        
Ogden, Utah Facility          
Loss Contingencies [Line Items]          
Loss contingency liability, current   $ 2.8      
Estimated insurance recoveries   2.3      
Goderich Plan Facility          
Loss Contingencies [Line Items]          
Loss contingency liability, current   45.6 $ 51.8    
Estimated insurance recoveries   45.3 47.0    
Loss contingency liability, noncurrent   $ 4.4 $ 0.0    
v3.26.1
OPERATING SEGMENTS - Narrative (Details)
 6 Months Ended
Mar. 31, 2025
segment
Segment Reporting [Abstract]  
Number of reportable segments 2
v3.26.1
OPERATING SEGMENTS - Schedule of Segment Information (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Feb. 02, 2026
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Segment Reporting Information [Line Items]          
Sales   $ 453.2 $ 494.6 $ 849.3 $ 801.8
Gross profit   83.0 76.8 146.2 111.1
Selling, general and administrative expenses   27.0 29.6 53.6 62.9
Loss on impairments   0.0 53.0 0.0 53.0
Other operating income   0.0 (2.7) 0.0 (2.2)
Operating income (loss)   56.0 (3.1) 92.6 (2.6)
Depreciation, depletion and amortization   28.2 26.5 54.6 53.3
Loss on sale of business, net   14.6 0.0 14.6 0.0
Total assets (as of end of period)   1,365.3 1,531.9 1,365.3 1,531.9
Capital expenditures   41.0 35.8    
Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOP Facility          
Segment Reporting Information [Line Items]          
Loss on sale of business, net $ 14.6        
Shipping and handling cost          
Segment Reporting Information [Line Items]          
Cost   138.0 151.4 250.1 232.0
Product cost          
Segment Reporting Information [Line Items]          
Cost   232.2 266.4 453.0 458.7
Operating Segments | Salt          
Segment Reporting Information [Line Items]          
Sales   382.6 432.7 714.1 674.9
Gross profit   72.8 76.5 128.5 113.3
Selling, general and administrative expenses   7.6 9.1 14.2 16.5
Loss on impairments     0.0   0.0
Other operating income     0.5   0.5
Operating income (loss)   65.2 66.9 114.3 96.3
Depreciation, depletion and amortization   18.0 17.4 36.1 34.9
Loss on sale of business, net   0.0   0.0  
Total assets (as of end of period)   825.3 959.2 825.3 959.2
Capital expenditures   31.0 27.5    
Operating Segments | Salt | Shipping and handling cost          
Segment Reporting Information [Line Items]          
Cost   128.7 141.9 232.5 213.2
Operating Segments | Salt | Product cost          
Segment Reporting Information [Line Items]          
Cost   181.1 214.3 353.1 348.4
Operating Segments | Plant Nutrition          
Segment Reporting Information [Line Items]          
Sales   67.0 58.3 127.8 119.7
Gross profit   9.0 0.2 15.2 (2.1)
Selling, general and administrative expenses   1.4 2.0 2.2 2.8
Loss on impairments     0.0   0.0
Other operating income     0.0   0.0
Operating income (loss)   7.6 (1.8) 13.0 (4.9)
Depreciation, depletion and amortization   9.3 7.4 16.7 14.9
Loss on sale of business, net   14.6   14.6  
Total assets (as of end of period)   338.2 365.7 338.2 365.7
Capital expenditures   9.2 6.2    
Operating Segments | Plant Nutrition | Shipping and handling cost          
Segment Reporting Information [Line Items]          
Cost   9.3 9.5 17.6 18.8
Operating Segments | Plant Nutrition | Product cost          
Segment Reporting Information [Line Items]          
Cost   48.7 48.6 95.0 103.0
Corporate & Other          
Segment Reporting Information [Line Items]          
Sales   3.6 3.6 7.4 7.2
Gross profit   1.2 0.1 2.5 (0.1)
Selling, general and administrative expenses   18.0 18.5 37.2 43.6
Loss on impairments     53.0   53.0
Other operating income     (3.2)   (2.7)
Operating income (loss)   (16.8) (68.2) (34.7) (94.0)
Depreciation, depletion and amortization   0.9 1.7 1.8 3.5
Loss on sale of business, net   0.0   0.0  
Total assets (as of end of period)   201.8 207.0 201.8 207.0
Capital expenditures   0.8 2.1    
Corporate & Other | Shipping and handling cost          
Segment Reporting Information [Line Items]          
Cost   0.0 0.0 0.0 0.0
Corporate & Other | Product cost          
Segment Reporting Information [Line Items]          
Cost   2.4 3.5 4.9 7.3
Intersegment Eliminations          
Segment Reporting Information [Line Items]          
Sales   (2.0) (2.3) (3.0) (5.5)
Intersegment Eliminations | Salt          
Segment Reporting Information [Line Items]          
Sales   0.0 0.0 0.0 0.0
Intersegment Eliminations | Plant Nutrition          
Segment Reporting Information [Line Items]          
Sales   $ 2.0 $ 2.3 $ 3.0 $ 5.5
v3.26.1
OPERATING SEGMENTS - Schedule of Disaggregated Revenue by Product Type (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Feb. 02, 2026
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Segment Reporting Information [Line Items]          
Sales to external customers   $ 453.2 $ 494.6 $ 849.3 $ 801.8
Loss on sale of business, net   14.6 0.0 14.6 0.0
Cumulative foreign currency translation adjustments   (13.1) 0.0 (13.1) 0.0
Impairment     53.0   53.0
Production recall expense     0.9   1.8
Severance costs     4.0   4.0
Disposal Group, Disposed of by Sale, Not Discontinued Operations | SOP Facility          
Segment Reporting Information [Line Items]          
Loss on sale of business, net $ 14.6        
Cumulative foreign currency translation adjustments $ 13.1        
Highway Deicing Salt          
Segment Reporting Information [Line Items]          
Sales to external customers   278.9 324.8 489.7 462.9
Consumer & Industrial Salt          
Segment Reporting Information [Line Items]          
Sales to external customers   103.7 107.9 224.4 212.0
SOP          
Segment Reporting Information [Line Items]          
Sales to external customers   69.0 60.6 130.8 125.2
Eliminations & Other          
Segment Reporting Information [Line Items]          
Sales to external customers   1.6 1.3 4.4 1.7
Operating Segments | Salt          
Segment Reporting Information [Line Items]          
Sales to external customers   382.6 432.7 714.1 674.9
Loss on sale of business, net   0.0   0.0  
Operating Segments | Plant Nutrition          
Segment Reporting Information [Line Items]          
Sales to external customers   67.0 58.3 127.8 119.7
Loss on sale of business, net   14.6   14.6  
Operating Segments | Highway Deicing Salt | Salt          
Segment Reporting Information [Line Items]          
Sales to external customers   278.9 324.8 489.7 462.9
Operating Segments | Highway Deicing Salt | Plant Nutrition          
Segment Reporting Information [Line Items]          
Sales to external customers   0.0 0.0 0.0 0.0
Operating Segments | Consumer & Industrial Salt | Salt          
Segment Reporting Information [Line Items]          
Sales to external customers   103.7 107.9 224.4 212.0
Operating Segments | Consumer & Industrial Salt | Plant Nutrition          
Segment Reporting Information [Line Items]          
Sales to external customers   0.0 0.0 0.0 0.0
Operating Segments | SOP | Salt          
Segment Reporting Information [Line Items]          
Sales to external customers   0.0 0.0 0.0 0.0
Operating Segments | SOP | Plant Nutrition          
Segment Reporting Information [Line Items]          
Sales to external customers   69.0 60.6 130.8 125.2
Operating Segments | Eliminations & Other | Salt          
Segment Reporting Information [Line Items]          
Sales to external customers   0.0 0.0 0.0 0.0
Operating Segments | Eliminations & Other | Plant Nutrition          
Segment Reporting Information [Line Items]          
Sales to external customers   (2.0) (2.3) (3.0) (5.5)
Corporate & Other          
Segment Reporting Information [Line Items]          
Sales to external customers   3.6 3.6 7.4 7.2
Loss on sale of business, net   0.0   0.0  
Corporate & Other | Highway Deicing Salt          
Segment Reporting Information [Line Items]          
Sales to external customers   0.0 0.0 0.0 0.0
Corporate & Other | Consumer & Industrial Salt          
Segment Reporting Information [Line Items]          
Sales to external customers   0.0 0.0 0.0 0.0
Corporate & Other | SOP          
Segment Reporting Information [Line Items]          
Sales to external customers   0.0 0.0 0.0 0.0
Corporate & Other | Eliminations & Other          
Segment Reporting Information [Line Items]          
Sales to external customers   $ 3.6 $ 3.6 $ 7.4 $ 7.2
v3.26.1
STOCKHOLDERS’ EQUITY AND EQUITY INSTRUMENTS - Narrative (Details)
$ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2026
USD ($)
shares
Mar. 31, 2025
USD ($)
Mar. 31, 2026
USD ($)
wk
shares
Mar. 31, 2025
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of weeks for grant | wk     50  
Selling, General and Administrative Expenses        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based payment arrangement, expense | $ $ 2.2 $ 2.8 $ 4.5 $ 6.7
Equity Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based payment arrangement, nonvested award, option, cost not yet recognized, amount | $ $ 12.7   $ 12.7  
Share-based payment arrangement, nonvested award, cost not yet recognized, period for recognition     1 year 8 months 12 days  
RSUs        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, non-option equity instruments, granted (in shares)     478,287  
Number of shares available from conversion (in shares) 1   1  
RSUs | Director        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, non-option equity instruments, granted (in shares)     33,068  
RSUs | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Performance period     1 year  
RSUs | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Performance period     3 years  
Deferred Stock Units (DSUs) | Director        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, non-option equity instruments, granted (in shares)     16,982  
Stock Payments        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Reissued share of treasury stock (in shares)     8,971  
Deferred Stock Unit        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, non-option equity instruments, granted (in shares)     4,076  
Scorecard PSUs        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation arrangement by share-based payment award, non-option equity instruments, granted (in shares)     182,071  
Performance period     3 years  
Modifier change     20.00%  
Dividend yield     0.00%  
Scorecard PSUs | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation payment award performance percentage     0.00%  
Expected volatility     48.00%  
Risk-free rate of return     3.50%  
Scorecard PSUs | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation payment award performance percentage     200.00%  
Stock Options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Performance period     4 years  
Number of shares available from conversion (in shares) 1   1  
Award expiration period     7 years  
v3.26.1
STOCKHOLDERS’ EQUITY AND EQUITY INSTRUMENTS - Schedule of Stock-Based Compensation Activity (Details)
$ / shares in Units, $ in Millions
 6 Months Ended
Mar. 31, 2026
USD ($)
$ / shares
shares
Stock Options  
Number  
Outstanding at beginning of period (in shares) 107,261
Granted (in shares) 0
Released from restriction (in shares) 0
Cancelled/expired (in shares) (794)
Outstanding at end of period (in shares) 106,467
Weighted-average exercise price  
Weighted-average exercise price at beginning of period (in dollars per share) | $ / shares $ 63.43
Weighted-average exercise price, granted (in dollars per share) | $ / shares 0
Weighted-average exercise price, released from restriction (in dollars per share) | $ / shares 0
Weighted-average exercise price, cancelled/expired (in dollars per share) | $ / shares 67.50
Weighted-average exercise price at end of period (in dollars per share) | $ / shares $ 63.40
RSUs  
Number  
Outstanding at beginning of period (in shares) 828,922
Granted (in shares) 478,287
Released from restriction (in shares) (318,033)
Cancelled/expired (in shares) (15,573)
Outstanding at end of period (in shares) 973,603
Weighted-average fair value  
Weighted-average fair value at beginning of period (in dollars per share) | $ / shares $ 15.34
Weighted-average fair value, granted (in dollars per share) | $ / shares 18.47
Weighted-average fair value, released from restriction (in dollars per share) | $ / shares 15.69
Weighted-average fair value, cancelled/expired (in dollars per share) | $ / shares 24.43
Weighted-average fair value at end of period (in dollars per share) | $ / shares $ 16.63
PSUs  
Number  
Outstanding at beginning of period (in shares) 316,480
Granted (in shares) 182,071
Released from restriction (in shares) 0
Cancelled/expired (in shares) 0
Outstanding at end of period (in shares) 498,551
Weighted-average fair value  
Weighted-average fair value at beginning of period (in dollars per share) | $ / shares $ 16.89
Weighted-average fair value, granted (in dollars per share) | $ / shares 19.37
Weighted-average fair value, released from restriction (in dollars per share) | $ / shares 0
Weighted-average fair value, cancelled/expired (in dollars per share) | $ / shares 0
Weighted-average fair value at end of period (in dollars per share) | $ / shares $ 17.80
PSU at grant date (in shares per unit) 1
Equity Awards  
Weighted-average fair value  
Fair value of stock withheld related to vesting of RSUs and PSUs | $ $ 1.7
v3.26.1
STOCKHOLDERS’ EQUITY AND EQUITY INSTRUMENTS - Schedule of Components and Changes in Accumulated Other Comprehensive Income (Loss) (Details)
$ in Millions
 6 Months Ended
Mar. 31, 2026
USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]  
Beginning Balance $ 234.1
Other comprehensive loss before reclassifications (7.9)
Amounts reclassified from AOCL 14.0
Net current period other comprehensive income (loss) 6.1
Ending Balance 274.2
Unrealized foreign currency translation adjustments 0.2
Total  
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]  
Beginning Balance (107.9)
Ending Balance (101.8)
Gains and (Losses) on Cash Flow Hedges  
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]  
Beginning Balance (0.8)
Other comprehensive loss before reclassifications (1.7)
Amounts reclassified from AOCL 0.5
Net current period other comprehensive income (loss) (1.2)
Ending Balance (2.0)
Benefit Plans | Defined Benefit Pension  
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]  
Beginning Balance (6.3)
Other comprehensive loss before reclassifications 0.0
Amounts reclassified from AOCL 0.4
Net current period other comprehensive income (loss) 0.4
Ending Balance (5.9)
Benefit Plans | Other Post-Employment Benefits  
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]  
Beginning Balance 1.8
Other comprehensive loss before reclassifications 0.0
Amounts reclassified from AOCL 0.0
Net current period other comprehensive income (loss) 0.0
Ending Balance 1.8
Foreign Currency  
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]  
Beginning Balance (102.6)
Other comprehensive loss before reclassifications (6.2)
Amounts reclassified from AOCL 13.1
Net current period other comprehensive income (loss) 6.9
Ending Balance $ (95.7)
v3.26.1
DERIVATIVE FINANCIAL INSTRUMENTS - Narrative (Details)
MMBTU in Millions, $ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Mar. 31, 2026
USD ($)
Mar. 31, 2025
USD ($)
Mar. 31, 2026
USD ($)
MMBTU
Mar. 31, 2025
USD ($)
Sep. 30, 2025
MMBTU
Derivatives, Fair Value [Line Items]          
Net gains to be reclassified from accumulated other comprehensive loss to earnings during the next 12 months     $ 1.8    
Commodity Contract          
Derivatives, Fair Value [Line Items]          
Notional amount (in MMBtus) | MMBTU     2.5   2.6
Commodity Contract | Derivatives Designated as Hedging Instruments          
Derivatives, Fair Value [Line Items]          
Percent of forecasted usage to be hedged 90.00%   90.00%    
Maximum period which the company hedges in advance of forecasted purchase     36 months    
Natural Gas Instruments, Net | Derivatives Designated as Hedging Instruments | Cash Flow Hedging          
Derivatives, Fair Value [Line Items]          
Net cash expense in product cost $ 0.0 $ 0.4 $ 0.5 $ 1.0  
v3.26.1
DERIVATIVE FINANCIAL INSTRUMENTS - Schedule of Fair Value of Derivatives (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Derivatives, Fair Value [Line Items]    
Asset Derivatives $ 5.8 $ 7.9
Liability Derivatives 7.8 8.7
Commodity Contract    
Derivatives, Fair Value [Line Items]    
Netting of contracts in a receivable position against contracts in payable position 4.3 7.8
Commodity Contract | Derivatives Designated as Hedging Instruments | Other current assets    
Derivatives, Fair Value [Line Items]    
Asset Derivatives 4.3 6.2
Commodity Contract | Derivatives Designated as Hedging Instruments | Accrued expenses and other current liabilities    
Derivatives, Fair Value [Line Items]    
Liability Derivatives 6.1 7.1
Commodity Contract | Derivatives Designated as Hedging Instruments | Other assets    
Derivatives, Fair Value [Line Items]    
Asset Derivatives 1.5 1.7
Commodity Contract | Derivatives Designated as Hedging Instruments | Other noncurrent liabilities    
Derivatives, Fair Value [Line Items]    
Liability Derivatives 1.7 $ 1.6
Other Contract    
Derivatives, Fair Value [Line Items]    
Netting of contracts in a receivable position against contracts in payable position $ 1.5  
v3.26.1
FAIR VALUE MEASUREMENTS - Schedule of Estimated Fair Values for Type of Instrument (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Mar. 31, 2026
Sep. 30, 2025
Asset Class:    
Mutual fund investments in a non-qualified savings plan $ 3.6 $ 3.5
Total assets at fair value 9.4 11.4
Liability Class:    
Liabilities related to non-qualified savings plan 3.6 3.5
Total liabilities at fair value $ 11.4 $ 12.2
Common Stock, Large Cap US Companies | Mutual Fund Investments, Concentration Risk | Investment Benchmark    
Liability Class:    
Investment concentration risk (as a percent) 34.00% 29.00%
Common Stock of Small to Mid Cap US Companies | Mutual Fund Investments, Concentration Risk | Investment Benchmark    
Liability Class:    
Investment concentration risk (as a percent) 4.00% 4.00%
Common Stock, International Companies | Mutual Fund Investments, Concentration Risk | Investment Benchmark    
Liability Class:    
Investment concentration risk (as a percent) 2.00% 2.00%
Bond Funds | Mutual Fund Investments, Concentration Risk | Investment Benchmark    
Liability Class:    
Investment concentration risk (as a percent) 9.00% 9.00%
Short-Term Investments | Mutual Fund Investments, Concentration Risk | Investment Benchmark    
Liability Class:    
Investment concentration risk (as a percent) 16.00% 20.00%
Blended Funds | Mutual Fund Investments, Concentration Risk | Investment Benchmark    
Liability Class:    
Investment concentration risk (as a percent) 35.00% 36.00%
Derivatives Designated as Hedging Instruments    
Asset Class:    
Derivatives – natural gas instruments, net $ 5.8 $ 7.9
Liability Class:    
Derivatives - natural gas instruments, net 7.8 8.7
Quoted Prices in Active Market (Level One)    
Asset Class:    
Mutual fund investments in a non-qualified savings plan 3.6 3.5
Total assets at fair value 3.6 3.5
Liability Class:    
Liabilities related to non-qualified savings plan 3.6 3.5
Total liabilities at fair value 3.6 3.5
Quoted Prices in Active Market (Level One) | Derivatives Designated as Hedging Instruments    
Asset Class:    
Derivatives – natural gas instruments, net 0.0 0.0
Liability Class:    
Derivatives - natural gas instruments, net 0.0 0.0
Significant Other Observable Inputs (Level Two)    
Asset Class:    
Mutual fund investments in a non-qualified savings plan 0.0 0.0
Total assets at fair value 5.8 7.9
Liability Class:    
Liabilities related to non-qualified savings plan 0.0 0.0
Total liabilities at fair value 7.8 8.7
Significant Other Observable Inputs (Level Two) | Derivatives Designated as Hedging Instruments    
Asset Class:    
Derivatives – natural gas instruments, net 5.8 7.9
Liability Class:    
Derivatives - natural gas instruments, net 7.8 8.7
Significant Unobservable Inputs (Level Three)    
Asset Class:    
Mutual fund investments in a non-qualified savings plan 0.0 0.0
Total assets at fair value 0.0 0.0
Liability Class:    
Liabilities related to non-qualified savings plan 0.0 0.0
Total liabilities at fair value 0.0 0.0
Significant Unobservable Inputs (Level Three) | Derivatives Designated as Hedging Instruments    
Asset Class:    
Derivatives – natural gas instruments, net 0.0 0.0
Liability Class:    
Derivatives - natural gas instruments, net $ 0.0 $ 0.0
v3.26.1
FAIR VALUE MEASUREMENTS - Schedule of Fair value in the Statement of Financial Position (Details) - Senior Notes - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Jun. 16, 2025
Nov. 30, 2019
0.08 Senior Notes due July 2030        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Stated interest rate 8.00% 8.00% 8.00%  
Debt fair value amount $ 650.0 $ 650.0    
0.08 Senior Notes due July 2030 | Quoted Prices in Active Market (Level One)        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt fair value amount 0.0 0.0    
0.08 Senior Notes due July 2030 | Significant Other Observable Inputs (Level Two)        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt fair value amount 671.9 680.1    
0.08 Senior Notes due July 2030 | Significant Unobservable Inputs (Level Three)        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt fair value amount $ 0.0 $ 0.0    
6.75% Senior Notes due December 2027        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Stated interest rate 6.75% 6.75%   6.75%
Debt fair value amount   $ 150.0    
6.75% Senior Notes due December 2027 | Quoted Prices in Active Market (Level One)        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt fair value amount   0.0    
6.75% Senior Notes due December 2027 | Significant Other Observable Inputs (Level Two)        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt fair value amount   150.1    
6.75% Senior Notes due December 2027 | Significant Unobservable Inputs (Level Three)        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Debt fair value amount   $ 0.0    
v3.26.1
SUPPLEMENTAL BALANCE SHEET INFORMATION - Schedule of Other Current Assets (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Current assets:    
Prepaid taxes $ 19.1 $ 9.7
Other 12.9 11.2
Total other current assets 32.0 20.9
Other noncurrent assets    
Operating lease right-of-use assets, net 48.8 52.3
Raw materials and supplies, net of allowance 32.9 33.0
Deposits 2.8 43.8
Other 14.1 18.2
Total other noncurrent assets $ 98.6 $ 147.3
v3.26.1
SUPPLEMENTAL BALANCE SHEET INFORMATION - Schedule of Other Liabilities (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Sep. 30, 2025
Accrued expenses and other current liabilities    
Accrued expenses $ 39.9 $ 36.5
Legal and environmental liabilities 45.6 51.8
Current portion of operating lease liabilities 15.8 14.7
Other taxes payable 6.0 7.7
Accrued expenses and other current liabilities 107.3 110.7
Other noncurrent liabilities    
Noncurrent portion of operating lease liabilities 34.3 39.2
Tax contingencies 15.5 67.4
Other 23.7 19.4
Total other noncurrent liabilities $ 73.5 $ 126.0
v3.26.1
NET INCOME (LOSS) PER SHARE (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Numerator:        
Net income (loss) $ 12.7 $ (32.0) $ 31.3 $ (55.6)
Less: net income allocated to participating securities (0.2) 0.0 (0.6) 0.0
Net income (loss) available to common stockholders, basic 12.5 (32.0) 30.7 (55.6)
Net income (loss) available to common stockholders, diluted $ 12.5 $ (32.0) $ 30.7 $ (55.6)
Denominator (in thousands):        
Weighted-average common shares outstanding for basic net income (loss) per share (in shares) 42,160 41,521 42,105 41,480
Weighted-average effect of dilutive equity awards outstanding (in shares) 197 0 192 0
Shares for diluted net income (loss) per share (in shares) 42,357 41,521 42,297 41,480
Basic net income (loss) per common share (in dollars per share) $ 0.30 $ (0.77) $ 0.73 $ (1.34)
Diluted net income (loss) per common share (in dollars per share) $ 0.30 $ (0.77) $ 0.73 $ (1.34)
Net income was allocated to weighted participating securities (in shares) 889,000   792,000  
Stock Options        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive weighted options outstanding (in shares) 869,000 1,298,000 770,000 1,227,000
v3.26.1
RELATED PARTY TRANSACTIONS (Details) - USD ($)
 3 Months Ended 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Sep. 30, 2025
Related Party Transaction [Line Items]          
Total sales $ 453,200,000 $ 494,600,000 $ 849,300,000 $ 801,800,000  
Total receivables 223,300,000   223,300,000   $ 179,600,000
Accounts payable 100,800,000   100,800,000   96,000,000.0
Purchased of salt-treatment materials 1,100,000   2,200,000    
Koch, Inc.          
Related Party Transaction [Line Items]          
Total sales 400,000 $ 800,000 900,000 $ 1,900,000  
Total receivables 0.0   0.0   200,000
Accounts payable 0   0   $ 0
Related Party          
Related Party Transaction [Line Items]          
Accounts payable $ 100,000   $ 100,000