Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Oct. 24, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Penumbra Inc
Entity Central Index Key	0001321732
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		34,503,038

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 47,742	$ 50,637
Marketable investments	146,176	163,954
Accounts receivable, net of doubtful accounts of $2,054 and $1,290 at September 30, 2018 and December 31, 2017, respectively	80,435	58,007
Inventories	109,706	94,901
Prepaid expenses and other current assets	13,536	14,735
Total current assets	397,595	382,234
Property and equipment, net	34,133	30,899
Intangible assets, net	27,284	23,778
Goodwill	7,923	8,178
Long-term investments (Note 3)	0	3,872
Deferred taxes	32,985	26,690
Other non-current assets	1,085	1,016
Total assets	501,005	476,667
Current liabilities:
Accounts payable	8,869	6,757
Accrued liabilities	56,183	44,825
Total current liabilities	65,052	51,582
Deferred rent	7,510	6,199
Other non-current liabilities	19,155	18,478
Total liabilities	91,717	76,259
Commitments and contingencies
Stockholders’ equity:
Common stock	34	33
Additional paid-in capital	407,881	396,810
Accumulated other comprehensive (loss) income	(899)	1,569
Retained earnings	2,403	1,996
Total Penumbra, Inc. stockholders’ equity	409,419	400,408
Non-controlling interest	(131)	0
Total stockholders’ equity	409,288	400,408
Total liabilities and stockholders’ equity	$ 501,005	$ 476,667

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 2,054	$ 1,290

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenue	$ 111,806	$ 83,911	$ 324,145	$ 237,713
Cost of revenue	36,794	29,134	110,324	84,298
Gross profit	75,012	54,777	213,821	153,415
Operating expenses:
Research and development	9,092	8,132	25,298	23,260
Sales, general and administrative	55,934	45,962	165,209	132,846
Acquired in-process research and development	30,835	0	30,835	0
Total operating expenses	95,861	54,094	221,342	156,106
(Loss) income from operations	(20,849)	683	(7,521)	(2,691)
Interest income, net	771	658	2,240	1,926
Other income (expense), net	170	(102)	(460)	(665)
(Loss) income before income taxes and equity in losses of unconsolidated investee	(19,908)	1,239	(5,741)	(1,430)
Provision for (benefit from) income taxes	1,598	456	(5,288)	2,293
(Loss) income before equity in losses of unconsolidated investee	(21,506)	783	(453)	(3,723)
Equity in losses of unconsolidated investee	(920)	(545)	(3,101)	(703)
Consolidated net (loss) income	(22,426)	238	(3,554)	(4,426)
Net loss attributable to non-controlling interest	(3,496)	0	(3,496)	0
Net (loss) income attributable to Penumbra, Inc.	$ (18,930)	$ 238	$ (58)	$ (4,426)
Net (loss) income per share attributable to common stockholders — Basic (in dollars per share)	$ (0.55)	$ 0.01	$ 0.00	$ (0.14)
Net (loss) income per share attributable to common stockholders — Diluted (in dollars per share)	$ (0.55)	$ 0.01	$ 0.00	$ (0.14)
Weighted average shares used to compute net (loss) income per share attributable to common stockholders — Basic (in shares)	34,248,484	33,446,841	34,057,216	32,766,135
Weighted average shares used to compute net (loss) income per share attributable to common stockholders — Diluted (in shares)	34,248,484	35,664,272	34,057,216	32,766,135

Condensed Consolidated Statements of Comprehensive (Loss) Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Consolidated net (loss) income	$ (22,426)	$ 238	$ (3,554)	$ (4,426)
Other comprehensive (loss) income, net of tax:
Foreign currency translation adjustments, net of tax	(353)	5,845	(2,367)	5,771
Net change in unrealized gains (losses) on available-for-sale securities, net of tax	115	54	(101)	121
Total other comprehensive (loss) income, net of tax	(238)	5,899	(2,468)	5,892
Consolidated comprehensive (loss) income	(22,664)	6,137	(6,022)	1,466
Net loss attributable to non-controlling interest	(3,496)	0	(3,496)	0
Comprehensive (loss) income attributable to Penumbra, Inc.	$ (19,168)	$ 6,137	$ (2,526)	$ 1,466

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Statement of Cash Flows [Abstract]
Consolidated net loss	$ (3,554)	$ (4,426)
Adjustments to reconcile consolidated net (loss) to net cash provided by operating activities:
Depreciation and amortization	4,459	2,580
(Accretion of discount) amortization of premium on marketable investments	(69)	501
Stock-based compensation	13,551	13,092
Loss on non-marketable equity investments	3,101	703
Provision for doubtful accounts	833	445
Inventory write-downs	1,046	996
Deferred taxes	(6,411)	1
Acquired in-process research and development	30,835	0
Change in fair value of contingent consideration	852	0
Other	64	28
Changes in operating assets and liabilities:
Accounts receivable	(23,284)	704
Inventories	(15,395)	(14,716)
Prepaid expenses and other current and non-current assets	733	3,303
Accounts payable	1,688	873
Accrued expenses and other non-current liabilities	12,828	9,514
Net cash provided by operating activities	21,277	13,598
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments to Acquire Assets and Businesses, Net of Cash Acquired	19,914	9,253
Contributions to non-marketable investments	(1,382)	(5,130)
Purchase of marketable investments	(96,969)	(139,317)
Proceeds from sales of marketable investments	12,131	28,167
Proceeds from maturities of marketable investments	102,687	73,579
Acquisition of intangible assets from a licensing agreement	0	2,500
Purchases of property and equipment	(6,563)	(6,805)
Net cash used in investing activities	(10,010)	(61,259)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock upon underwritten public offering, net of issuance cost	0	106,265
Proceeds from exercises of stock options	4,294	4,244
Proceeds from issuance of stock under employee stock purchase plan	3,584	2,914
Payment of employee taxes related to vested restricted stock	(16,021)	(10,569)
Payment of acquisition-related obligations	(4,431)	0
Other	(409)	(940)
Net cash (used in) provided by financing activities	(12,983)	101,914
Effect of foreign exchange rate changes on cash and cash equivalents	(1,179)	(1,868)
NET (DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(2,895)	52,385
CASH AND CASH EQUIVALENTS—Beginning of period	50,637	13,236
CASH AND CASH EQUIVALENTS—End of period	47,742	65,621
NONCASH INVESTING AND FINANCING ACTIVITIES:
Common shares issued as consideration in connection with a buyout agreement (Notes 6, 8 and 9)	5,256	0
Purchase of property and equipment funded through accounts payable and accrued liabilities	1,378	2,933
Asset acquisition (Note 3) or business combination related contingent liabilities and working capital adjustment liabilities (Note 5)	4,500	4,897
Licensing agreement related contingent liabilities	$ 0	$ 12,717

Organization and Description of Business	9 Months Ended
Organization and Description of Business	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	1. Organization and Description of Business Penumbra, Inc. (the “Company”) is a global healthcare company focused on innovative therapies. The Company designs, develops, manufactures and markets medical devices and has a broad portfolio of products that addresses challenging medical conditions and significant clinical needs.

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Consolidation The accompanying condensed consolidated balance sheet as of September 30, 2018, the condensed consolidated statements of operations for the three and nine months ended September 30, 2018 and 2017, the condensed consolidated statements of comprehensive (loss) income for the three and nine months ended September 30, 2018 and 2017, and the condensed consolidated statements of cash flows for the nine months ended September 30, 2018 and 2017 are unaudited. The unaudited condensed consolidated financial statements included herein have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and the applicable rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial information. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. The condensed consolidated balance sheet as of December 31, 2017 was derived from the audited financial statements as of that date. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements and, in the opinion of management, reflect all adjustments of a normal recurring nature considered necessary to state fairly the Company’s financial position as of September 30, 2018, the results of its operations for the three and nine months ended September 30, 2018 and 2017, and the cash flows for the nine months ended September 30, 2018 and 2017. The results for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 or for any other future annual or interim period. Certain changes in presentation were made in the condensed consolidated financial statements for the three and nine months ended September 30, 2017 to conform to the presentation for the three and nine months ended September 30, 2018. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2017, included in the Company’s Annual Report on Form 10-K. There have been no changes to the Company’s significant accounting policies during the nine months ended September 30, 2018, as compared to the significant accounting policies described in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017, other than changes to the Company’s revenue policy described below in connection with the adoption of the guidance under the Accounting Standards Codification (“ASC”) 606. The condensed consolidated financial statements include the accounts of the Company, its wholly-owned subsidiaries and its majority-owned subsidiary, MVI Health Inc. (“MVI”). On August 31, 2018, the Company acquired a controlling interest in MVI. The portion of equity not attributable to the Company is considered noncontrolling interest and was recorded at the fair value as of the acquisition date. The amounts attributable to non-controlling interest are classified separately in the condensed consolidated financial statements. Any subsequent changes in the Company’s ownership interest while the Company retains its controlling interest in MVI will be accounted for as equity transactions. Refer to Note “3. Investments and Fair Value of Financial Instruments” for more information on the asset acquisition of MVI. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and equity accounts; disclosure of contingent assets and liabilities at the date of the financial statements; and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates, including those related to marketable investments, provisions for doubtful accounts, the amount of variable consideration included in the transaction price, warranty reserve, valuation of inventories, useful lives of property and equipment, income taxes, contingent consideration and other contingencies, among others. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other data. Actual results could differ from those estimates. Revenue Recognition Revenue is comprised of product revenue net of returns, discounts, administration fees and sales rebates. The Company adopted the guidance under ASC 606 on January 1, 2018 using the modified retrospective method for all contracts not completed as of the date of adoption. Therefore, the comparative prior year information has not been adjusted and continues to be reported under ASC 605 with the impact of the adoption reflected in opening retained earnings. Under ASC 606, the Company recognizes revenue when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Revenue from product sales continue to be recognized either on the date of shipment or the date of receipt by the customer, but is deferred for certain transactions when control has not yet transferred. However, with respect to products that the Company consigns to hospitals, which primarily consist of coils, the Company recognizes revenue at the time hospitals utilize products in a procedure. Deferred revenue represents amounts that the Company has already invoiced its customers and that are ultimately expected to be recognized as revenue, but for which not all revenue recognition criteria have been met. As of September 30, 2018 and December 31, 2017, respectively, the Company's deferred revenue balance was not material. Revenue is recorded at the net sales price, which includes estimates of variable consideration such as product returns utilizing historical return rates, rebates, discounts, and other adjustments to net revenue. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price. Variable consideration is included in revenue only to the extent that it is probable that a significant reversal of the revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. The Company’s terms and conditions permit product returns and exchanges. The Company bases its estimates for sales returns on actual historical returns over the prior three years and they are recorded as reductions in revenue at the time of sale. Upon recognition, the Company reduces revenue and cost of revenue for the estimated return. Return rates can fluctuate over time, but are sufficiently predictable to allow the Company to estimate expected future product returns. For more information and disclosures on the Company’s revenue, refer to Note “13. Revenues.” Segments The Company determined its operating segment on the same basis that it uses to evaluate its performance internally. The Company has one business activity: the design, development, manufacturing and marketing of innovative devices, and operates as one operating segment. The Company’s chief operating decision-maker, its Chief Executive Officer, reviews its operating results for the purpose of allocating resources and evaluating financial performance. The Company assigns revenue to a geographic area based on the destination to which it ships its products. Recent Accounting Guidance Recently Adopted Accounting Standards In the first quarter of 2018, the Company adopted ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), and its associated amendments. Under the standard, revenue is recognized when a customer obtains control of promised goods or services in an amount that reflects the consideration the entity expects to receive in exchange for those goods or services. In addition, the standard requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The Company applied the five step method outlined in the ASU to all revenue streams and elected to utilize the modified retrospective implementation method. The additional disclosures required by the ASU have been included in Note “13. Revenues.” In the first quarter of 2018, the Company adopted ASU No. 2016-18, Statement of Cash Flows: Restricted Cash, a consensus of the Financial Accounting Standards Board (“FASB”) Emerging Issues Task Force. Under the standard, restricted cash and restricted cash equivalent amounts are presented within cash and cash equivalents when reconciling the total beginning and ending amounts shown on the statement of cash flows. When cash, cash equivalents, restricted cash and restricted cash equivalents are presented in more than one line item on the balance sheet, a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet is required. The adoption of this standard did not have a material impact to the statement of cash flow for the nine months ended September 30, 2017, as the Company did not hold any restricted cash as of September 30, 2017. In the first quarter of 2018, the Company adopted ASU No. 2017-09, Compensation - Stock Compensation - Scope of Modification Accounting. The standard provides clarification on when modification accounting should be used for changes to the terms or conditions of a share-based payment award. This standard does not change the accounting for modifications but clarifies that modification accounting guidance should only be applied if there is a change to the value, vesting conditions, or award classification and would not be required if the changes are considered non-substantive. The standard is effective for annual periods beginning after December 15, 2017, and interim periods within those annual periods. The guidance was adopted on a prospective basis in the first quarter of 2018 and did not have any impact upon adoption. In the first quarter of 2018, the Company adopted ASU No. 2018-02, Income Statement - Reporting Comprehensive Income. The standard allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017 (the “Tax Reform Act”). The standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted for any interim and annual financial statements that have not yet been issued. The Company elected to early adopt this standard on a prospective basis in the first quarter of 2018 and reclassify the stranded tax effects resulting from the Tax Reform Act from accumulated other comprehensive income to retained earnings. There were no additional income tax effects resulting from the Tax Reform Act reclassified from accumulated comprehensive income to retained earnings. The adoption of this standard did not have a material impact on the Company’s financial position. In the first quarter of 2018, the Company adopted ASU No. 2018-05, Income Taxes (Topic 740): Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118, which included amendments to expand income tax accounting and disclosure guidance pursuant to SEC Staff Accounting Bulletin No. 118 (“SAB 118”) issued by the SEC in December 2017. SAB 118 provides guidance on accounting for the income tax effects of the Tax Reform Act. Refer to Note “11. Income Taxes” for more information and disclosures related to this amended guidance. In the third quarter of 2018, the Company adopted ASU No. 2018-07, Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which simplifies the accounting and reporting for share-based payments granted to nonemployees for goods and services. Under the new guidance, payments to nonemployees would be more closely aligned with the requirements for share-based payments granted to employees. The standard is effective for annual periods beginning after December 15, 2018, and interim periods within those annual periods. Early adoption is permitted, but no earlier than the Company's adoption date of ASC 606. The Company adopted the standard on a prospective basis in the third quarter of 2018 and the adoption did not have a material impact on the Company’s financial statement. Recently Issued Accounting Standards In February 2016, the FASB issued ASU No. 2016-02, Leases, which amends the existing accounting standards for leases. In September 2017, the FASB issued ASU No. 2017-13 which provides additional clarification and implementation guidance on the previously issued ASU No. 2016-02. Under the new guidance, a lessee will be required to recognize a lease liability and right-of-use asset for all leases with terms in excess of twelve months. The new guidance also modifies the classification criteria and accounting for sales-type and direct financing leases, and requires additional disclosures to enable users of financial statements to understand the amount, timing, and uncertainty of cash flows arising from leases. Consistent with current guidance, a lessee’s recognition, measurement, and presentation of expenses and cash flows arising from a lease will continue to depend primarily on its classification. In July 2018, the FASB issued ASU No. 2018-10 and ASU No. 2018-11, which further clarifies the application of the guidance issued under ASU No. 2016-02 and provides updates to transition methods and practical expedients. ASU No. 2018-11 provides an optional transition method in addition to the existing transition method which allows entities, at the adoption date, to recognize a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. The accounting standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, and must be applied using a modified retrospective approach. Early adoption is permitted. While the Company is continuing to assess all potential impacts of the standard, it expects that most of its lease commitments will be subject to the updated standard and recognized as lease liabilities and right-of-use assets upon adoption. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses. The standard changes how entities will measure credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. The Company will recognize an allowance for credit losses on available-for-sale securities rather than deductions in amortized cost. The standard is effective for fiscal years and interim periods beginning after December 15, 2019. Early adoption is permitted for all periods beginning after December 15, 2018. The Company is currently evaluating the impact of adopting this standard. In August 2018, the FASB issued ASU 2018-13, Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). The primary focus of the standard is to improve the effectiveness of the disclosure requirements for fair value measurements. The standard is effective for fiscal years and interim periods beginning after December 15, 2019. An entity is permitted to early adopt the removed or modified disclosures upon the issuance of the standard and may delay adoption of the additional disclosures until their effective date. The Company is currently evaluating the impact of adopting this standard. In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532, Disclosure Update and Simplification. The final rule amends certain disclosure requirements that were redundant, duplicative, overlapping, outdated or superseded. In addition, the amendments expanded the disclosure requirements on the analysis of stockholders' equity for interim financial statements. Under the amendments, an analysis of changes in each caption of stockholders' equity presented in the balance sheet must be provided in a note or separate statement. The analysis should present a reconciliation of the beginning balance to the ending balance of each period for which a statement of comprehensive income is required to be filed. The Company anticipates its first presentation of changes in stockholders' equity will be included in its Form 10-Q for the quarter ended March 31, 2019.

Investments and Fair Value of Financial Instruments

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

3. Investments and Fair Value of Financial Instruments

Marketable Investments

The Company’s marketable investments have been classified and accounted for as available-for-sale. The Company’s marketable investments as of September 30, 2018 and December 31, 2017 were as follows (in thousands):



	September 30, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Commercial paper	$	12,660	$	—	$	(5	)	$	12,655
U.S. treasury	6,401		—		(37		)	6,364
U.S. agency and government sponsored securities	4,219		—		(34		)	4,185
U.S. states and municipalities	8,587		—		(23		)	8,564
Corporate bonds	114,746		60		(398		)	114,408
Total	$	146,613	$	60	$	(497	)	$	146,176



	December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Commercial paper	$	19,941	$	—	$	(8	)	$	19,933
U.S. treasury	6,402		—		(28		)	6,374
U.S. agency and government sponsored securities	4,787		—		(18		)	4,769
U.S. states and municipalities	12,510		—		(23		)	12,487
Corporate bonds	120,648		23		(280		)	120,391
Total	$	164,288	$	23	$	(357	)	$	163,954

The following tables present the gross unrealized losses and the fair value for those marketable investments that were in an unrealized loss position for less than twelve months or for twelve months or longer as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018
	Less than 12 months					12 months or more					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Commercial paper	$	12,655	$	(5	)	$	—	$	—		$	12,655	$	(5	)
U.S. treasury	4,371		(29		)	1,993		(8		)	6,364		(37		)
U.S. agency and government sponsored securities	4,185		(34		)	—		—			4,185		(34		)
U.S. states and municipalities	6,564		(23		)	—		—			6,564		(23		)
Corporate bonds	60,544		(244		)	13,191		(154		)	73,735		(398		)
Total	$	88,319	$	(335	)	$	15,184	$	(162	)	$	103,503	$	(497	)



	December 31, 2017
	Less than 12 months					12 months or more					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Commercial paper	$	19,933	$	(8	)	$	—	$	—		$	19,933	$	(8	)
U.S. treasury	6,374		(28		)	—		—			6,374		(28		)
U.S. agency and government sponsored securities	2,778		(9		)	1,991		(9		)	4,769		(18		)
U.S. states and municipalities	10,092		(23		)	—		—			10,092		(23		)
Corporate bonds	93,284		(188		)	10,201		(92		)	103,485		(280		)
Total	$	132,461	$	(256	)	$	12,192	$	(101	)	$	144,653	$	(357	)

The contractual maturities of the Company’s marketable investments as of September 30, 2018 and December 31, 2017 were as follows (in thousands):



	September 30, 2018		December 31, 2017
	Fair Value		Fair Value
Due in less than one year	$	96,143	$	104,272
Due in one to five years	50,033		59,682
Total	$	146,176	$	163,954

Non-Marketable Equity Investments

In the second quarter of 2017, the Company and Sixense Enterprises, Inc. (“Sixense”) formed MVI as a privately-held joint venture for the purpose of exploring healthcare applications of virtual reality technology, with each party holding 50% of the issued and outstanding equity of MVI. On August 31, 2018 (“Transfer Agreement Closing Date”), the Company entered into a Stock Transfer Agreement (the “Transfer Agreement”) between the Company, MVI and Sixense, to purchase an additional 40% of the equity interest in MVI from Sixense for an initial cash purchase price of $20.0 million, excluding the additional $4.5 million of probable future payments relating to an anti-dilution provision in the Transfer Agreement. Following the Transfer Agreement Closing Date, the Company owns a 90% equity interest in MVI and Sixense retains the remaining 10% equity interest.

Prior to the Transfer Agreement Closing Date, the Company accounted for its investment in MVI under the equity method and was not required to consolidate MVI. As of December 31, 2017 and through the nine months ended September 30, 2018, the Company determined that MVI was not a variable interest entity (“VIE”). Furthermore, pursuant to agreements between the parties at the time of MVI’s formation, the Company was obligated to perform certain services or make additional cash contributions to MVI for no additional equity interest. These services included, but were not limited to, information technology, accounting, other administrative services and research and development. The Company’s contributions made to prior to the Transfer Agreement Closing Date are presented as a component of “Contributions to non-marketable investments” in the condensed consolidated statements of cash flows.

As of December 31, 2017, the carrying value of the non-marketable equity investment was approximately $3.9 million, representing the Company’s contributions to MVI offset by the Company’s share of equity method investee losses, and is presented in long-term investments on the condensed consolidated balance sheet. During the three and nine months ended September 30, 2017, MVI had no revenue and recorded a net loss of $1.1 million and $1.4 million, respectively. During the three and nine months ended September 30, 2018, prior to the Transfer Agreement Closing Date, MVI had no revenue and recorded a net loss of $1.8 million and $6.2 million, respectively. The Company reflected its 50% share of MVI’s losses as equity in losses of unconsolidated investees in the condensed consolidated statements of operations through the Transfer Agreement Closing Date.

Impact of Transfer Agreement on Non-Marketable Equity Investments

The Company accounted for the Transfer Agreement as an asset acquisition, as it was determined that the transaction did not meet the definition of a business under the framework of the authoritative accounting guidance for business combinations. The total consideration transferred has been allocated to the non-monetary assets acquired and liabilities assumed based on their relative fair value.

The following table presents the components of the consideration transferred at fair value as of the Transfer Agreement Closing Date (amounts presented in thousands):



	Amount
Cash transferred	$	20,000
Anti-dilution protection at Transfer Agreement Closing Date	4,500
Carrying amount of Penumbra’s equity method investment in MVI	2,202
Fair value of the remaining non-controlling interest	3,365
Total consideration transferred	$	30,067

In addition to the cash transferred, the consideration included a probable contingent liability related to an anti-dilution provision whereby the Company may issue additional shares of MVI to Sixense with an aggregate value of up to $4.5 million. As of September 30, 2018, the current and non-current portion of the related liability was $2.0 million and $2.5 million, respectively. The consideration transferred also included the $2.2 million carrying amount of the Company’s equity method investment in MVI as of the Transfer Agreement Closing Date, which was written-off as part of the accounting for the Transfer Agreement. The Company also recorded $3.4 million in non-controlling interest on the condensed consolidated financial statements related to the fair value of the remaining equity interest held by Sixense as of the Transfer Agreement Closing Date.

The primary asset acquired in the Transfer Agreement constitutes an in-process research and development asset (“IPR&D”). Due to the nature of the other assets acquired and liabilities assumed, the difference between the fair value of the consideration transferred and the fair value of the tangible net assets acquired was allocated solely to the IPR&D. The Company recorded a charge of $30.8 million to acquired in-process research and development expense in the condensed consolidated statements of operations at the Transfer Agreement Closing Date because the Company determined that (1) MVI had not yet reached technological feasibility or had not yet reached the appropriate regulatory approval for any products and (2) the asset had no alternative future use as of the Transfer Agreement Closing Date. Following the Transfer Agreement Closing Date, the financial results of MVI have been consolidated into the accompanying condensed consolidated financial statements, with the amounts attributable to the non-controlling interest classified separately.

Fair Value of Financial Instruments

Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. The accounting guidance establishes a three-tiered hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value:

Level 1 - Quoted prices in active markets for identical assets or liabilities.

Level 2 - Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

The categorization of a financial instrument within the valuation hierarchy is based on the lowest level of input that is significant to the fair value measurement.

The Company classifies its cash equivalents and marketable investments within Level 1 and Level 2, as it uses quoted market prices or alternative pricing sources and models utilizing market observable inputs.

The Company determined the fair value of its Level 1 financial instruments, which are traded in active markets, using quoted market prices for identical instruments.

Financial instruments classified within Level 2 of the fair value hierarchy are valued based on other observable inputs, including broker or dealer quotations or alternative pricing sources. When quoted prices in active markets for identical assets or liabilities are not available, the Company relies on non-binding quotes from its investment managers, which are based on proprietary valuation models of independent pricing services. These models generally use inputs such as observable market data, quoted market prices for similar instruments, or historical pricing trends of a security relative to its peers. To validate the fair value determination provided by its investment managers, the Company reviews the pricing movement in the context of overall market trends and trading information from its investment managers. In addition, the Company assesses the inputs and methods used in determining the fair value in order to determine the classification of securities in the fair value hierarchy.

The following table sets forth the Company’s financial assets measured at fair value by level within the fair value hierarchy (in thousands):



	As of September 30, 2018
	Level 1		Level 2		Level 3		Fair Value
Financial Assets
Cash equivalents:
Commercial paper	$	—	$	8,978	$	—	$	8,978
Money market funds	5,055		—		—		5,055
Marketable investments:
Commercial paper	—		12,655		—		12,655
U.S. treasury	6,364		—		—		6,364
U.S. agency and government sponsored securities	—		4,185		—		4,185
U.S. states and municipalities	—		8,564		—		8,564
Corporate bonds	—		114,408		—		114,408
Total	$	11,419	$	148,790	$	—	$	160,209
Financial Liabilities:
Contingent consideration obligations⁽¹⁾	$	—	$	—	$	2,519	$	2,519
Total	$	—	$	—	$	2,519	$	2,519



	As of December 31, 2017
	Level 1		Level 2		Level 3		Fair Value
Financial Assets
Cash equivalents:
Commercial paper	$	—	$	9,185	$	—	$	9,185
Money market funds	2,264		—		—		2,264
Marketable investments:
Commercial paper	—		19,933		—		19,933
U.S. treasury	6,374		—		—		6,374
U.S. agency and government sponsored securities	—		4,769		—		4,769
U.S. states and municipalities	—		12,487		—		12,487
Corporate bonds	—		120,391		—		120,391
Total	$	8,638	$	166,765	$	—	$	175,403
Financial Liabilities:
Contingent consideration obligations⁽¹⁾	$	—	$	—	$	4,675	$	4,675
Total	$	—	$	—	$	4,675	$	4,675

⁽¹⁾More information on the contingent consideration obligations and the changes in fair value are presented below.

As of September 30, 2018, the Company’s contingent consideration liability is classified as a Level 3 measurement for which fair value is derived from various inputs, including forecasted revenues during the earn-out and milestone periods, revenue volatilities, discount rates, and estimates in the timing and likelihood of achieving revenue-based milestones. The fair value of the contingent consideration liability will be remeasured each reporting period. In addition to the revenue generated during the earn-out and milestone periods, the following table presents certain quantitative information about unobservable inputs used in the Level 3 fair value measurement of the Company’s contingent consideration liability:



	Fair Value at September 30, 2018 (in thousands)		Valuation Method	Unobservable Inputs	Input (range where applicable)
Crossmed: Revenue-based milestones	$	2,519	Monte Carlo Simulation	Earn-out period over which revenue-based milestone payments are made	2018 - 2019
				Risk-adjusted discount rate	15%
				Revenue volatilities for each type of revenue-based milestone	8.9% and 14.8%

The following table summarizes the changes in fair value of the contingent consideration obligation for the nine months ended September 30, 2018 (in thousands):



Fair Value of Contingent Consideration Obligation	Crossmed⁽¹⁾
Balance at December 31, 2017	$	4,675
Additional contingent consideration liabilities	—
Payments of contingent consideration liabilities	(3,017		)
Changes in fair value	851
Foreign currency remeasurement	10
Balance at September 30, 2018	$	2,519

⁽¹⁾During the three and nine months ended September 30, 2018, the fair value of the contingent consideration obligation related to the acquisition of Crossmed S.p.A. (“Crossmed”) increased by $0.1 million and $0.9 million, respectively, which was recorded in sales, general and administrative expense in the condensed consolidated statements of operations. The fair value of the contingent consideration increased as a result of updates to the underlying forecasts based on actual results to date and changes in estimates. For more information refer to Note “5. Business Combination.”

During the three and nine months ended September 30, 2018 and 2017, the Company did not record impairment charges related to its marketable investments and the Company did not hold any Level 3 marketable investments as of September 30, 2018 or December 31, 2017. Also, during the nine months ended September 30, 2018 and 2017, the Company did not have any transfers between Level 1, Level 2 or Level 3 of the fair value hierarchy. The Company did not have any financial assets and liabilities measured at fair value on a non-recurring basis as of September 30, 2018 or December 31, 2017.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Balance Sheet Components

9 Months Ended

Sep. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Balance Sheet Components

4. Balance Sheet Components

Inventories

The following table shows the components of inventories as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018		December 31, 2017
Raw materials	$	16,930	$	13,529
Work in process	9,751		6,073
Finished goods	83,025		75,299
Inventories	$	109,706	$	94,901

Accrued Liabilities

The following table shows the components of accrued liabilities as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018		December 31, 2017
Payroll and employee-related cost	$	32,088	$	22,001
Sales return provision	3,000		3,035
Preclinical and clinical trial cost	1,112		1,514
Royalty	819		1,115
Product warranty	1,808		1,088
Leasehold improvement expenditures	860		1,012
Acquisition-related costs⁽¹⁾	3,711		4,752
Other accrued liabilities	12,785		10,308
Total accrued liabilities	$	56,183	$	44,825

⁽¹⁾Acquisition-related costs consist of the current portion of contingent liabilities related to (1) the cash milestone payments and working capital adjustment liabilities for the acquisition of Crossmed and (2) an anti-dilution provision for the asset acquisition of MVI. Refer to Note “5. Business Combination” for more information on the acquisition of Crossmed and Note “3. Investments and Fair Value of Financial Instruments” for more information on the MVI asset acquisition.

The following table shows the changes in the Company’s estimated product warranty accrual, included in accrued liabilities, as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018			December 31, 2017
Balance at the beginning of the period	$	1,088		$	1,254
Accruals of warranties issued	1,131			471
Settlements of warranty claims	(411		)	(637		)
Balance at the end of the period	$	1,808		$	1,088

Other Non-Current Liabilities

The following table shows the components of other non-current liabilities as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018		December 31, 2017
Deferred tax liabilities	$	3,235	$	3,299
Licensing-related cost⁽¹⁾	11,423		12,717
Asset acquisition-related costs⁽²⁾	2,500		—
Other non-current liabilities	1,997		2,462
Total other non-current liabilities	$	19,155	$	18,478

⁽¹⁾ Amount relates to the non-current liability recorded for probable future milestone payments to be made under the licensing agreement described in Note “6. Intangible Assets.” Refer therein for more information.

⁽²⁾Asset acquisition-related costs represents the non-current portion of the probable contingent liability related to an anti-dilution provision for the asset acquisition of MVI. Refer to Note “3. Investments and Fair Value of Financial Instruments” for more information on the MVI asset acquisition.

Business Combination

9 Months Ended

Sep. 30, 2018

Business Combinations [Abstract]

Business Combination

5. Business Combination

On July 3, 2017 (the “Closing Date”), the Company completed the acquisition of Crossmed, a joint stock company organized under the laws of Italy. Crossmed is engaged in the business of distributing medical supplies and equipment in Italy, San Marino, the Vatican, and Switzerland. Crossmed was the Company’s exclusive distributor in Italy, San Marino and the Vatican and the acquisition provides the Company with a direct relationship with its customers in these regions. As of the Closing Date, Crossmed became a wholly-owned subsidiary of the Company and was integrated into the Company’s core business. The acquisition of Crossmed did not result in any changes to the Company’s operating or reportable segment structure and the Company continues to operate as one operating segment.

The following table summarizes the Closing Date fair value of the consideration transferred, reflecting the measurement period adjustments recorded in the fourth quarter of 2017 (in thousands):



Cash, net of working capital and financial debt adjustments	$	11,088
Fair value of contingent consideration for milestone payments	4,343
Contract purchase price	$	15,431
Consideration for settlement of pre-existing receivable due from Crossmed to Penumbra	3,273
Total value of consideration transferred	$	18,704

On the Closing Date, the Company paid the sellers of Crossmed an initial payment of €8.2 million, or approximately $9.4 million, subject to post-closing adjustments for working capital and financial debt. The Company is also obligated to pay additional consideration in the form of milestone payments based on Crossmed’s net revenue, and may be required to pay additional consideration based on incremental net revenue, for the year ended December 31, 2017, and each of the years ending December 31, 2018 and 2019. There is no limit on the milestone payments that can be paid out. During the nine months ended September 30, 2018, the Company made $4.4 million in cash payments to the Sellers, of which $3.0 million related to the achievement of the 2017 milestones and the remainder related to working capital and financial debt adjustments. These payments have been presented as a component of financing activities in the condensed consolidated statement of cash flows due to the nature and timing of the payments.

As of September 30, 2018, the fair value of the current and non-current portion of the related liabilities for the future cash milestone payments recorded on the condensed consolidated balance sheet was $1.3 million and $1.2 million, respectively. For more information with respect to the nature and fair value of the Company’s contingent consideration obligations, refer to Note “3. Investments and Fair Value of Financial Instruments.”

The purchase price measurement period was closed as of June 30, 2018. The following table presents the allocation of the purchase price for Crossmed, reflecting the measurement period adjustments recorded in 2017 (in thousands):



	Acquisition-Date Fair Value			Estimated Useful Life of Finite-Lived Intangible Assets
Tangible assets acquired and (liabilities) assumed:
Accounts receivable	$	4,406
Inventories	1,343
Other current and non-current assets	1,596
Property and equipment, net	829
Accounts payable	(740		)
Accrued liabilities and obligations for short-term debt and credit facilities	(1,868		)
Deferred tax liabilities	(2,472		)
Other non-current liabilities	(797		)
Intangible assets acquired:
Customer relationships	$	6,790		15 years
Other	1,750			5 years
Goodwill	7,867
Total purchase price	$	18,704

Acquired intangible assets are classified as Level 3 measurements for which fair value is derived from valuations based on inputs that are unobservable and significant to the overall fair value measurement. The Company used the income approach, specifically the discounted cash flow method and the incremental cash flow approach, to derive the fair value of the customer relationships and other intangible assets. Customer relationships are direct relationships with physicians and hospitals performing procedures with the distributed products. Other intangibles consist of non-Penumbra supplier relationships and sub-distributor relationships with third parties used to sell products, both as of the Closing Date. The intangible assets are amortized on a straight-line basis over their assigned estimated useful lives. The amortization of the acquired intangible assets are not deductible for tax purposes. As a result, a $2.5 million deferred tax liability was recorded as of the Closing Date.

The goodwill arising from the Crossmed acquisition is primarily attributed to expected synergies from future growth and assembled workforce. Goodwill will not be deductible for tax purposes.

Goodwill

9 Months Ended

Sep. 30, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill

7. Goodwill

The following table presents the changes in goodwill during the nine months ended September 30, 2018 (in thousands):



	Total Company
Balance as of December 31, 2017	$	8,178
Foreign currency translation	(255		)
Balance as of September 30, 2018	$	7,923

Goodwill Impairment Review

The Company reviews goodwill for impairment annually during the fourth quarter, on October 31st, or more frequently if events or circumstances indicate that an impairment loss may have occurred. During the nine months ended September 30, 2018, there were no events or changes in circumstances which triggered an impairment review.

Intangible Assets

9 Months Ended

Sep. 30, 2018

Intangible Assets, Net (Excluding Goodwill) [Abstract]

Intangible Assets

6. Intangible Assets

Acquired Intangible Assets

The following table presents details of the Company’s acquired finite-lived and indefinite-lived intangible assets, as of September 30, 2018 and December 31, 2017 (in thousands, except weighted-average amortization period):



As of September 30, 2018	Weighted-Average Amortization Period	Gross Carrying Amount		Accumulated Amortization			Net
Customer relationships	15.0 years	$	6,919	$	(576	)	$	6,343
Trade secrets and processes	20.0 years	5,256		(197		)	5,059
Other	5.0 years	1,784		(446		)	1,338
Total intangible assets subject to amortization	15.9 years	$	13,959	$	(1,219	)	$	12,740
Intangible assets related to licensed technology		14,544		—			14,544
Total intangible assets		$	28,503	$	(1,219	)	$	27,284



As of December 31, 2017	Weighted-Average Amortization Period	Gross Carrying Amount		Accumulated Amortization			Net
Customer relationships	15.0 years	$	7,141	$	(238	)	$	6,903
Other	5.0 years	1,841		(183		)	1,658
Total intangible assets subject to amortization	13.1 years	$	8,982	$	(421	)	$	8,561
Intangible assets related to licensed technology		15,217		—			15,217
Total intangible assets		$	24,199	$	(421	)	$	23,778

The customer relationships and other intangible assets subject to amortization relate to the acquisition of Crossmed during the third quarter of 2017. The gross carrying amount and accumulated amortization of these intangible assets are subject to foreign currency translation effects. Refer to Note “5. Business Combination” for more information. The Company’s $5.3 million trade secrets and processes intangible asset was recognized in connection with a royalty buyout agreement during the first quarter of 2018, which is discussed further in Note “8. Commitments and Contingencies” and Note “9. Stockholders’ Equity.”

The following table presents the amortization recorded related to the Company’s finite-lived intangible assets (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cost of revenue	$	66	$	—	$	197	$	—
Sales, general and administrative	205		258		631		258
Total	$	271	$	258	$	828	$	258

Licensed technology

During the third quarter of 2017, the Company entered into an exclusive technology license agreement (the “License Agreement”) that required the Company to pay an upfront payment to the licensor of $2.5 million and future revenue milestone-based payments on sales of products covered by the licensed intellectual property. The Company recorded an intangible asset equal to the total payments made and expected to be made under the License Agreement and a corresponding contingent liability for the probable future milestone payments not yet paid. The licensed technology is accounted for as an indefinite-lived intangible asset. Once regulatory approval is received to market and commercialize products utilizing the underlying technology, the Company will begin amortizing the intangible asset.

At the end of each reporting period the Company adjusts the contingent liabilities to reflect the amount of future milestone payments that are probable to be paid. Prior to the commercialization of products utilizing the underlying technology, any changes in the contingent liability are recorded as an adjustment between the liability balances and the gross carrying amount of the indefinite-lived intangible asset. During the three and nine months ended September 30, 2018, the contingent liability related to the exclusive technology license agreement increased by $0.3 million and decreased by $0.7 million, respectively. The changes in the contingent liability balance were due to changes in the underlying revenue forecasts used to estimate the probable future milestone payments. As of September 30, 2018, the balance of the contingent liability related to probable future milestone payments under the Licensing Agreement was $12.0 million, of which $0.6 million and $11.4 million were included in accrued liabilities and other non-current liabilities on the condensed consolidated balance sheet, respectively.

As of September 30, 2018, the gross carrying amount of the indefinite-lived intangible asset was $14.5 million. During the nine months ended September 30, 2018, the Company noted no events or circumstances that indicate the carrying value of the licensed technology may no longer be recoverable and that an impairment loss may have occurred.

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Lease Commitments The Company leases its offices primarily under non-cancelable operating leases that expire at various dates through 2031, subject to its option to renew certain leases for an additional 5 to 15 years. Rent expense for non-cancelable operating leases with scheduled rent increases is recognized on a straight-line basis over the lease term. Rent expense for the three months ended September 30, 2018 and 2017 was $1.4 million and $1.4 million, respectively, and for the nine months ended September 30, 2018 and 2017 was $4.3 million and $4.3 million, respectively. In addition, the Company’s lease commitments also require it to make additional payments during the lease term for taxes, insurance and other operating expenses. The Company leases other equipment and vehicles primarily under non-cancelable operating leases that expire at various dates through 2021. Royalty Obligations In March 2005, the Company entered into a license agreement that requires the Company to make minimum royalty payments to the licensor on a quarterly basis. As of both September 30, 2018 and December 31, 2017, the license agreement required minimum annual royalty payments of $0.1 million in equal quarterly installments. On each January 1, the quarterly calendar year minimum royalty shall be adjusted to equal the prior year’s minimum royalty adjusted by a percentage equal to the percentage change in the “consumer price index for all urban consumers” for the prior calendar year as reported by the U.S. Department of Labor. Unless terminated earlier, the term of the license agreement shall continue until the expiration of the last to expire patent that covers that licensed product or for the period of 15 years following the first commercial sale of such licensed product, whichever is longer. The first commercial sale of covered products occurred in June 2007. In April 2012, the Company entered into an agreement that requires the Company to pay, on a quarterly basis, a 5% royalty on sales of products covered under applicable patents. The first commercial sale of covered products occurred in April 2014. Unless terminated earlier, the royalty term for each applicable product shall continue for 15 years following the first commercial sale of such patented product, or when the applicable patent covering such product has expired, whichever is sooner. In November 2013, the Company entered into an agreement that required the Company to pay, on a quarterly basis, a 3% royalty on the first $5.0 million in sales and a 1% royalty on sales thereafter of products covered under applicable patents. The agreement was terminated effective January 1, 2018. In April 2015, the Company entered into a royalty agreement that required the Company to pay a 2% royalty on sales of certain products covered by the agreement, on a quarterly basis, in exchange for certain trade secrets and processes which were used to develop such covered products. The Company began the first commercial sale of the covered products in July 2015. In the first quarter of 2018, the Company entered into a buyout of this agreement (the “Buyout Agreement”) in which future royalty payments were canceled in exchange for shares of the Company’s common stock with a fair value of $5.3 million. The Company recorded an intangible asset equal to the $5.3 million buyout amount which will be amortized into cost of sales over the period in which the Company receives future economic benefit. After determining that the pattern of future cash flows associated with this intangible asset could not be reliably estimated with a high level of precision, the Company concluded that the intangible asset will be amortized on a straight‑line basis over its estimated useful life. For more information refer to Note “6. Intangible Assets” and Note “9. Stockholders’ Equity.” Royalty expense included in cost of revenue for the three months ended September 30, 2018 and 2017, was $0.9 million and $1.0 million, respectively, and for the nine months ended September 30, 2018 and 2017 was $2.4 million and $3.0 million, respectively. Contingencies From time to time, the Company may have certain contingent liabilities that arise in the ordinary course of business. The Company accrues a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. Refer to Note “3. Investments and Fair Value of Financial Instruments,” Note “5. Business Combination” and Note “6. Intangible Assets” for more information on contingent liabilities recorded on the condensed consolidated balance sheet. Indemnification The Company enters into standard indemnification arrangements in the ordinary course of business. In many such arrangements, the Company agrees to indemnify, hold harmless, and reimburse the indemnified parties for losses suffered or incurred by the indemnified parties in connection with any trade secret, copyright, patent or other intellectual property infringement claim by any third-party with respect to the Company’s technology. The Company also agrees to indemnify many purchasers for product defect and similar claims. The term of these indemnification agreements is generally perpetual. The maximum potential amount of future payments the Company could be required to make under these agreements is not determinable because it involves claims that may be made against the Company in the future, but have not yet been made. The Company has entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers, other than liabilities arising from willful misconduct of the individual. The Company has not incurred costs to defend lawsuits or settle claims related to these indemnification agreements. No liability associated with any of these indemnification requirements has been recorded to date. Litigation From time to time, the Company is subject to other claims and assessments in the ordinary course of business. The Company is not currently a party to any such litigation matter that, individually or in the aggregate, is expected to have a material adverse effect on the Company’s business, financial condition, results of operations or cash flows.

Stockholder's Equity

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stockholder's Equity

9. Stockholders’ Equity

Common Stock

In the first quarter of 2017, the Company issued and sold an aggregate of 1,495,000 shares of common stock at a public offering price of $76.00 per share, less the underwriters’ discounts and commissions, pursuant to an underwritten public offering. The Company received approximately $106.3 million in net cash proceeds after deducting underwriting discounts and commissions of $6.8 million and other offering expenses of $0.5 million.

In the first quarter of 2018, the Company issued 53,256 fully vested restricted stock units with a fair value of $5.3 million in connection with the Buyout Agreement, as discussed in Note “6. Intangible Assets” and Note “8. Commitments and Contingencies.” The Company recorded the $5.3 million fair value of the shares issued to additional-paid in capital on the condensed consolidated balance sheet upon the issuance of the awards, with the associated expense being amortized into cost of sales over the period in which the Company receives future economic benefit from the buyout.

Equity Incentive Plans

Stock Options

Activity of stock options under the Penumbra, Inc. 2005 Stock Plan, the Penumbra, Inc. 2011 Equity Incentive Plan and the Amended and Restated Penumbra, Inc. 2014 Equity Incentive Plan (collectively the “Plans”) during the nine months ended September 30, 2018 is set forth below:



	Number of Shares		Weighted-Average Exercise Price
Balance at December 31, 2017	2,107,104		$	17.58
Exercised	(348,316	)	12.32
Canceled/Forfeited	(2,014	)	22.04
Balance at September 30, 2018	1,756,774		18.62

Restricted Stock and Restricted Stock Units

Activity of unvested restricted stock and restricted stock units under the Plans during the nine months ended September 30, 2018 is set forth below:



	Number of Shares		Weighted -Average Grant Date Fair Value
Unvested at December 31, 2017	742,405		$	38.86
Granted	109,021		110.33
Vested	(376,284	)	38.67
Canceled/Forfeited	(3,625	)	80.11
Unvested at September 30, 2018	471,517		55.21

As of September 30, 2018, 460,432 restricted stock and restricted stock units are expected to vest.

Stock-based Compensation

The following table sets forth the stock-based compensation expense included in the Company’s condensed consolidated statements of operations for the three and nine months ended September 30, 2018 and 2017 (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cost of revenue	$	260	$	316	$	677	$	817
Research and development	405		352		1,148		913
Sales, general and administrative	3,747		3,819		11,726		11,362
Total	$	4,412	$	4,487	$	13,551	$	13,092

As of September 30, 2018, total unrecognized compensation cost was $23.7 million related to unvested share-based compensation arrangements which is expected to be recognized over a weighted average period of 2.2 years.

The total stock-based compensation cost capitalized in inventory was $0.4 million and $0.2 million as of September 30, 2018 and December 31, 2017, respectively.

Accumulated Other Comprehensive Income (Loss)

9 Months Ended

Sep. 30, 2018

Equity [Abstract]

Accumulated Other Comprehensive Income (Loss)

10. Accumulated Other Comprehensive (Loss) Income

Other comprehensive (loss) income consists of two components: unrealized gains or losses on the Company’s available-for-sale marketable investments and gains or losses from foreign currency translation adjustments. Until realized and reported as a component of net (loss) income, these comprehensive income (loss) items accumulate and are included within accumulated other comprehensive (loss) income. Unrealized gains and losses on the Company’s marketable investments are reclassified from accumulated other comprehensive (loss) income into earnings when realized upon sale, and are determined based on specific identification of securities sold. Gains and losses from the translation of assets and liabilities denominated in non-U.S. dollar functional currencies are included in accumulated other comprehensive (loss) income.

The following table summarizes the changes in the accumulated balances during the three and nine months ended September 30, 2018 and September 30, 2017, and includes information regarding the manner in which the reclassifications out of accumulated other comprehensive (loss) income into earnings affect the Company’s condensed consolidated statements of operations and condensed consolidated statements of comprehensive (loss) income (in thousands):



	Three Months Ended September 30, 2018									Three Months Ended September 30, 2017
	Marketable Investments			Currency Translation Adjustments			Total			Marketable Investments			Currency Translation Adjustments			Total
Balance at beginning of the period	$	(451	)	$	(210	)	$	(661	)	$	(38	)	$	(4,657	)	$	(4,695	)
Other comprehensive (loss) income before reclassifications:
Unrealized gain— marketable investments	151			—			151			54			—			54
Foreign currency translation (losses)	—			(353		)	(353		)	—			5,845			5,845
Income tax effect — (expense)	(36		)	—			(36		)	—			—			—
Net of tax	115			(353		)	(238		)	54			5,845			5,899
Amounts reclassified from accumulated other comprehensive income to earnings:
Realized gains — marketable investments	—			—			—			—			—			—
Income tax effect — (expense)	—			—			—			—			—			—
Net of tax	—			—			—			—			—			—
Net current-year other comprehensive income (loss)	115			(353		)	(238		)	54			5,845			5,899
Balance at end of the period	$	(336	)	$	(563	)	$	(899	)	$	16		$	1,188		$	1,204



	Nine Months Ended September 30, 2018									Nine Months Ended September 30, 2017
	Marketable Investments			Currency Translation Adjustments			Total			Marketable Investments			Currency Translation Adjustments			Total
Balance at beginning of the period	$	(235	)	$	1,804		$	1,569		$	(105	)	$	(4,583	)	$	(4,688	)
Other comprehensive (loss) income before reclassifications:
Unrealized (losses) gain— marketable investments	(102		)	—			(102		)	157			—			157
Foreign currency translation (losses)	—			(2,145		)	(2,145		)	—			5,771			5,771
Income tax effect — benefit (expense)	1			(222		)	(221		)	—			—			—
Net of tax	(101		)	(2,367		)	(2,468		)	157			5,771			5,928
Amounts reclassified from accumulated other comprehensive income to earnings:
Realized (losses)— marketable investments	—			—			—			(36		)	—			(36		)
Income tax effect — expense	—			—			—			—			—			—
Net of tax	—			—			—			(36		)	—			(36		)
Net current-year other comprehensive (loss) income	(101		)	(2,367		)	(2,468		)	121			5,771			5,892
Balance at end of the period	$	(336	)	$	(563	)	$	(899	)	$	16		$	1,188		$	1,204

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes The Company’s income tax expense, deferred tax assets and liabilities, and reserves for unrecognized tax benefits reflect management’s best assessment of estimated current and future taxes to be paid. The Company is subject to income taxes in both the United States and foreign jurisdictions. Significant judgment and estimates are required in determining the consolidated income tax expense. During interim periods, the Company generally utilizes the estimated annual effective tax rate method which involves the use of forecasted information. Under this method, the provision is calculated by applying an estimate of the annual effective tax rate for the full fiscal year to “ordinary” income or loss (pretax income or loss excluding unusual or infrequently occurring discrete items) for the reporting period. Jurisdictions with tax assets for which the Company believes a tax benefit cannot be realized are excluded from the computation of its annual effective tax rate. During the three months ended September 30, 2018, the Company acquired a controlling interest in MVI which was accounted for as an asset acquisition for financial statement purposes. As a result, the Company recorded a charge of $30.8 million to acquired in-process research and development expense in the condensed consolidated statements of operations at the Transfer Agreement Closing Date, which is not deductible for tax purposes. Refer to Note “3. Investments and Fair Value of Financial Instruments” for more information on the MVI asset acquisition. The Company considers this expense a significant unusual and infrequently occurring item. As a result, the $30.8 million charge was excluded from the calculation of the Company’s estimated annual effective tax rate. The Company’s provision for income taxes was a $1.6 million tax expense for the three months ended September 30, 2018, compared to a $0.5 million tax expense for the three months ended September 30, 2017. The Company’s effective tax rate changed to (8.0)% for the three months ended September 30, 2018, compared to 36.8% for the three months ended September 30, 2017. The Company’s provision for income taxes was a $5.3 million tax benefit in the nine months ended September 30, 2018, compared to a $2.3 million tax expense in the nine months ended September 30, 2017. The Company’s effective tax rate changed to 92.1% for the nine months ended September 30, 2018, compared to (160.3)% for the nine months ended September 30, 2017. The Company’s provision for/(benefit from) income taxes for the three and nine months ended September 30, 2018 was primarily due to excess tax benefits from stock-based compensation attributable to the Company’s US jurisdiction, income taxes attributable to the Company’s profits in its foreign jurisdictions, and a discrete tax charge resulting from the acquired in-process research and development expense associated with the MVI asset acquisition which is not deductible for tax purposes. The Company’s provision for income taxes in the three and nine months ended September 30, 2017 was primarily due to income taxes attributable to the Company’s foreign jurisdictions, and the tax impact from recognizing the deferred tax assets associated with intra-entity asset transfers. The tax benefits attributable to the Company’s US jurisdiction were excluded from its tax provision for the three and nine months ended September 30, 2017 due to the partial valuation allowance recorded against the Company’s domestic DTAs as of September 30, 2017. On December 22, 2017, the Tax Reform Act was enacted. The Tax Reform Act significantly revised the U.S. corporate income tax regime by, including but not limited to, lowering the U.S. corporate income tax rate to 21% effective January 1, 2018, implementing a territorial tax system, imposing a one-time transition tax on previously untaxed accumulated earnings and profits of foreign subsidiaries, and creating new taxes on foreign sourced earnings. Also on December 22, 2017, the Securities and Exchange Commission issued Staff Accounting Bulletin 118 (“SAB 118”), which provides guidance on accounting for tax effects of the Tax Reform Act. SAB 118 provides a measurement period, that should not extend beyond one year from the Tax Reform Act enactment date, for companies to complete the accounting under ASC 740. In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Tax Reform Act for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Reform Act is incomplete but it is able to determine a reasonable estimate, it must record a provisional estimate to be included in the financial statements. In the nine months ended September 30, 2018, the Company recorded a provisional tax charge for the deemed repatriation tax on the undistributed earnings of its foreign subsidiaries. The Company also made sufficient progress on its global intangible low-taxed income tax analysis to reasonably estimate the effects, and therefore reflected provisional amounts in the Company’s financial statements for the nine months ended September 30, 2018. Recording estimates of the tax impact of the deemed repatriation and the global intangible low-taxed income did not have a material effect on the Company’s financial statements. The final impact of the Tax Reform Act may differ from these estimates, due to, among other things, changes in the Company’s interpretations and assumptions, and additional guidance that may be issued. With the adoption of ASU 2016-09, additional deferred tax assets (“DTAs”) of NOL and credit carryforwards were created. With any DTAs, an assessment is necessary to determine if sufficient taxable income will be generated to realize the DTAs and, if not, a substantial valuation allowance to reduce the DTAs may be required. The Company assessed its ability to realize the benefits of its domestic DTAs by evaluating all available positive and negative evidence, objective and subjective in nature, including (1) cumulative results of operations in recent years, (2) sources of recent pre-tax income, (3) estimates of future taxable income, and (4) the length of net operating loss (“NOL”) carryforward periods. The Company considered its projections of future taxable income in conjunction with relevant provisions of the Tax Reform Act, and concluded that sufficient future taxable income will be generated to realize the benefits of its federal DTAs prior to expiration other than its federal research and development tax credit DTAs. The Company’s federal research and development tax credit DTAs, which have a 20 year carryforward period, are expected to expire prior to utilization based on future projected taxable income. As a result, the Company maintains a valuation allowance against its federal research and development tax credit DTAs as of September 30, 2018. Consistent with prior periods, the Company maintained a full valuation allowance against its California DTAs as of September 30, 2018.

Net Income (Loss) per Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Net Income (Loss) per Share

12. Net (loss) income attributable to Penumbra, Inc. per Share

The Company’s basic net (loss) income attributable to Penumbra, Inc. per share is calculated by dividing the net (loss) income attributable to Penumbra, Inc. by the weighted average number of shares of common stock outstanding for the period. The diluted net (loss) income per share is computed by giving effect to all potential dilutive common stock equivalents outstanding for the period. For purposes of this calculation, options to purchase common stock, restricted stock, restricted stock units and stock sold through the Company’s employee stock purchase plan are considered common stock equivalents.

A reconciliation of the numerator and denominator used in the calculation of the basic and diluted (loss) income per share for the three and nine months ended September 30, 2018 and 2017 is as follows (in thousands, except share and per share amounts):



	Three Months Ended September 30,					Nine Months Ended September 30,
	2018			2017		2018			2017
Numerator:
Net (loss) income attributable to Penumbra, Inc.	$	(18,930	)	$	238	$	(58	)	$	(4,426	)
Denominator:
Weighted average shares used to compute net income (loss):
Basic	34,248,484			33,446,841		34,057,216			32,766,135
Effect of dilutive securities from stock-based benefit plans, as calculated using treasury stock method	—			2,217,431		—			—
Diluted	34,248,484			35,664,272		34,057,216			32,766,135
Net (loss) income attributable to Penumbra, Inc. per share from:
Basic	$	(0.55	)	$	0.01	$	—		$	(0.14	)
Diluted	$	(0.55	)	$	0.01	$	—		$	(0.14	)

Outstanding common stock equivalents of 2.3 million and 21 thousand shares for the three months ended September 30, 2018 and 2017, respectively, and 2.3 million and 3.0 million shares for the nine months ended September 30, 2018 and 2017, respectively, were excluded from the computation of diluted net (loss) income attributable to Penumbra Inc. per share because their effect would have been anti-dilutive.

Revenues

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Revenues

13. Revenues

Adoption of ASC Topic 606, “Revenue from Contracts with Customers”

The Company adopted the guidance under ASC 606 on January 1, 2018 using the modified retrospective method for all contracts not completed as of the date of adoption. Therefore, the comparative prior year information has not been adjusted and continues to be reported under ASC 605 with the impact of the adoption reflected in opening retained earnings. As a result of adoption, the cumulative impact to our retained earnings at January 1, 2018 was $0.3 million.

The adoption of ASC 606 represents a change in accounting principle that more closely aligns the timing of revenue recognition with the point in time that a performance obligation is satisfied. The Company’s performance obligations are satisfied at a point in time. The implementation of the new standard did not have a material impact on the measurement or recognition of revenue from prior periods, however additional disclosures have been added in accordance with the guidance.

As required by ASC 606, the impact of adoption of the new revenue standard on the Company's condensed consolidated statements of operations and comprehensive income and condensed consolidated balance sheets was as follows (in thousands):



	As of September 30, 2018
				Adjusted Balance
	As Reported	Adjustments		Without 606 Adoption
Consolidated Balance Sheet Data:
Assets
Accounts receivable, net of doubtful accounts	80,435	(921	)	79,514
Inventories	109,706	314		110,020
Deferred taxes	32,985	198		33,183
Equity
Retained Earnings	2,403	(409	)	1,994



	Three Months Ended September 30, 2018						Nine Months Ended September 30, 2018
					Adjusted Balance						Adjusted Balance
	As Reported		Adjustments		Without 606 Adoption		As Reported		Adjustments		Without 606 Adoption
Consolidated Income Statement Data:
Revenue	111,806		(23	)	111,783		324,145		(263	)	323,882
Cost of revenue	36,794		(9	)	36,785		110,324		(97	)	110,227
Income (loss) from operations	(20,849	)	(14	)	(20,863	)	(7,521	)	(166	)	(7,687	)
Income (loss) before income taxes and equity in losses of unconsolidated investee	(19,908	)	(14	)	(19,922	)	(5,741	)	(166	)	(5,907	)
(Benefit from) provision for income taxes	1,598		(5	)	1,593		(5,288	)	(54	)	(5,342	)
Net income (loss) attributable to Penumbra, Inc.	(18,930	)	(9	)	(18,939	)	(58	)	(112	)	(170	)

Revenue Recognition

Revenue is recognized in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. All revenue recognized in the income statement is considered to be revenue from contracts with customers.

The Company’s revenues disaggregated by geography, based on the destination to which the Company ships its products, for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
United States	$	72,991	$	55,652	$	210,070	$	157,559
Japan	10,131		8,499		31,427		24,483
Other International	28,684		19,760		82,648		55,671
Total	$	111,806	$	83,911	$	324,145	$	237,713

The Company’s revenues disaggregated by product category, for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Neuro	$	74,689	$	58,670	$	220,318	$	165,122
Peripheral Vascular	37,117		25,241		103,827		72,591
Total	$	111,806	$	83,911	$	324,145	$	237,713

Performance Obligations

Delivery of Penumbra products - Penumbra’s contracts with customers typically contain a single performance obligation, delivery of Penumbra products. Satisfaction of that performance obligation occurs when control of the promised goods transfers to the customer, which is generally upon shipment for non-consignment sale agreements and upon utilization for consignment sale agreements.

Payment terms - Our payment terms vary by the type and location of our customer. The timing between fulfillment of performance obligations and when payment is due is not significant and does not give rise to financing transactions. The Company did not have any contracts with significant financing components as of September 30, 2018.

Product returns - The Company may allow customers to return products purchased at the Company’s discretion. The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized. The Company currently estimates product return liabilities using its own historic sales information, trends, industry data, and other relevant data points.

Warranties - Penumbra offers its standard warranty to all customers and it is not available for sale on a standalone basis. Penumbra’s standard warranty represents its guarantee that its products function as intended, are free from defects, and comply with agreed-upon specifications and quality standards. This assurance does not constitute a service and is not a separate performance obligation.

Transaction Price

Revenue is recorded at the net sales price, which includes estimates of variable consideration such as product returns utilizing historical return rates, rebates, discounts, and other adjustments to net revenue. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price. When determining if variable consideration should be constrained, management considers whether there are factors that could result in a significant reversal of revenue and the likelihood of a potential reversal. Variable consideration is included in revenue only to the extent that it is probable that a significant reversal of the revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. These estimates are re-assessed each reporting period as required. When the Company performs shipping and handling activities after control of goods is transferred to the customer, they are considered as fulfillment activities, and costs are accrued for when the related revenue is recognized. Taxes collected from customers relating to product sales and remitted to governmental authorities are excluded from revenues.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation and Consolidation The accompanying condensed consolidated balance sheet as of September 30, 2018, the condensed consolidated statements of operations for the three and nine months ended September 30, 2018 and 2017, the condensed consolidated statements of comprehensive (loss) income for the three and nine months ended September 30, 2018 and 2017, and the condensed consolidated statements of cash flows for the nine months ended September 30, 2018 and 2017 are unaudited. The unaudited condensed consolidated financial statements included herein have been prepared by the Company in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and the applicable rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial information. Accordingly, they do not include all of the information and notes required by U.S. GAAP for complete financial statements. The condensed consolidated balance sheet as of December 31, 2017 was derived from the audited financial statements as of that date. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements and, in the opinion of management, reflect all adjustments of a normal recurring nature considered necessary to state fairly the Company’s financial position as of September 30, 2018, the results of its operations for the three and nine months ended September 30, 2018 and 2017, and the cash flows for the nine months ended September 30, 2018 and 2017. The results for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the year ending December 31, 2018 or for any other future annual or interim period. Certain changes in presentation were made in the condensed consolidated financial statements for the three and nine months ended September 30, 2017 to conform to the presentation for the three and nine months ended September 30, 2018. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the audited consolidated financial statements and notes thereto for the year ended December 31, 2017, included in the Company’s Annual Report on Form 10-K. There have been no changes to the Company’s significant accounting policies during the nine months ended September 30, 2018, as compared to the significant accounting policies described in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017, other than changes to the Company’s revenue policy described below in connection with the adoption of the guidance under the Accounting Standards Codification (“ASC”) 606.
Consolidation	The condensed consolidated financial statements include the accounts of the Company, its wholly-owned subsidiaries and its majority-owned subsidiary, MVI Health Inc. (“MVI”). On August 31, 2018, the Company acquired a controlling interest in MVI. The portion of equity not attributable to the Company is considered noncontrolling interest and was recorded at the fair value as of the acquisition date. The amounts attributable to non-controlling interest are classified separately in the condensed consolidated financial statements. Any subsequent changes in the Company’s ownership interest while the Company retains its controlling interest in MVI will be accounted for as equity transactions. Refer to Note “3. Investments and Fair Value of Financial Instruments” for more information on the asset acquisition of MVI. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and equity accounts; disclosure of contingent assets and liabilities at the date of the financial statements; and the reported amounts of revenues and expenses during the reporting period. On an ongoing basis, the Company evaluates its estimates, including those related to marketable investments, provisions for doubtful accounts, the amount of variable consideration included in the transaction price, warranty reserve, valuation of inventories, useful lives of property and equipment, income taxes, contingent consideration and other contingencies, among others. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other data. Actual results could differ from those estimates.
Revenue Recognition	Revenue Recognition Revenue is comprised of product revenue net of returns, discounts, administration fees and sales rebates. The Company adopted the guidance under ASC 606 on January 1, 2018 using the modified retrospective method for all contracts not completed as of the date of adoption. Therefore, the comparative prior year information has not been adjusted and continues to be reported under ASC 605 with the impact of the adoption reflected in opening retained earnings. Under ASC 606, the Company recognizes revenue when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Revenue from product sales continue to be recognized either on the date of shipment or the date of receipt by the customer, but is deferred for certain transactions when control has not yet transferred. However, with respect to products that the Company consigns to hospitals, which primarily consist of coils, the Company recognizes revenue at the time hospitals utilize products in a procedure. Deferred revenue represents amounts that the Company has already invoiced its customers and that are ultimately expected to be recognized as revenue, but for which not all revenue recognition criteria have been met. As of September 30, 2018 and December 31, 2017, respectively, the Company's deferred revenue balance was not material. Revenue is recorded at the net sales price, which includes estimates of variable consideration such as product returns utilizing historical return rates, rebates, discounts, and other adjustments to net revenue. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price. Variable consideration is included in revenue only to the extent that it is probable that a significant reversal of the revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. The Company’s terms and conditions permit product returns and exchanges. The Company bases its estimates for sales returns on actual historical returns over the prior three years and they are recorded as reductions in revenue at the time of sale. Upon recognition, the Company reduces revenue and cost of revenue for the estimated return. Return rates can fluctuate over time, but are sufficiently predictable to allow the Company to estimate expected future product returns. For more information and disclosures on the Company’s revenue, refer to Note “13. Revenues.”
Segments	Segments The Company determined its operating segment on the same basis that it uses to evaluate its performance internally. The Company has one business activity: the design, development, manufacturing and marketing of innovative devices, and operates as one operating segment. The Company’s chief operating decision-maker, its Chief Executive Officer, reviews its operating results for the purpose of allocating resources and evaluating financial performance. The Company assigns revenue to a geographic area based on the destination to which it ships its products.
Recent Accounting Guidance	Recent Accounting Guidance Recently Adopted Accounting Standards In the first quarter of 2018, the Company adopted ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), and its associated amendments. Under the standard, revenue is recognized when a customer obtains control of promised goods or services in an amount that reflects the consideration the entity expects to receive in exchange for those goods or services. In addition, the standard requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The Company applied the five step method outlined in the ASU to all revenue streams and elected to utilize the modified retrospective implementation method. The additional disclosures required by the ASU have been included in Note “13. Revenues.” In the first quarter of 2018, the Company adopted ASU No. 2016-18, Statement of Cash Flows: Restricted Cash, a consensus of the Financial Accounting Standards Board (“FASB”) Emerging Issues Task Force. Under the standard, restricted cash and restricted cash equivalent amounts are presented within cash and cash equivalents when reconciling the total beginning and ending amounts shown on the statement of cash flows. When cash, cash equivalents, restricted cash and restricted cash equivalents are presented in more than one line item on the balance sheet, a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet is required. The adoption of this standard did not have a material impact to the statement of cash flow for the nine months ended September 30, 2017, as the Company did not hold any restricted cash as of September 30, 2017. In the first quarter of 2018, the Company adopted ASU No. 2017-09, Compensation - Stock Compensation - Scope of Modification Accounting. The standard provides clarification on when modification accounting should be used for changes to the terms or conditions of a share-based payment award. This standard does not change the accounting for modifications but clarifies that modification accounting guidance should only be applied if there is a change to the value, vesting conditions, or award classification and would not be required if the changes are considered non-substantive. The standard is effective for annual periods beginning after December 15, 2017, and interim periods within those annual periods. The guidance was adopted on a prospective basis in the first quarter of 2018 and did not have any impact upon adoption. In the first quarter of 2018, the Company adopted ASU No. 2018-02, Income Statement - Reporting Comprehensive Income. The standard allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017 (the “Tax Reform Act”). The standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted for any interim and annual financial statements that have not yet been issued. The Company elected to early adopt this standard on a prospective basis in the first quarter of 2018 and reclassify the stranded tax effects resulting from the Tax Reform Act from accumulated other comprehensive income to retained earnings. There were no additional income tax effects resulting from the Tax Reform Act reclassified from accumulated comprehensive income to retained earnings. The adoption of this standard did not have a material impact on the Company’s financial position. In the first quarter of 2018, the Company adopted ASU No. 2018-05, Income Taxes (Topic 740): Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118, which included amendments to expand income tax accounting and disclosure guidance pursuant to SEC Staff Accounting Bulletin No. 118 (“SAB 118”) issued by the SEC in December 2017. SAB 118 provides guidance on accounting for the income tax effects of the Tax Reform Act. Refer to Note “11. Income Taxes” for more information and disclosures related to this amended guidance. In the third quarter of 2018, the Company adopted ASU No. 2018-07, Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which simplifies the accounting and reporting for share-based payments granted to nonemployees for goods and services. Under the new guidance, payments to nonemployees would be more closely aligned with the requirements for share-based payments granted to employees. The standard is effective for annual periods beginning after December 15, 2018, and interim periods within those annual periods. Early adoption is permitted, but no earlier than the Company's adoption date of ASC 606. The Company adopted the standard on a prospective basis in the third quarter of 2018 and the adoption did not have a material impact on the Company’s financial statement. Recently Issued Accounting Standards In February 2016, the FASB issued ASU No. 2016-02, Leases, which amends the existing accounting standards for leases. In September 2017, the FASB issued ASU No. 2017-13 which provides additional clarification and implementation guidance on the previously issued ASU No. 2016-02. Under the new guidance, a lessee will be required to recognize a lease liability and right-of-use asset for all leases with terms in excess of twelve months. The new guidance also modifies the classification criteria and accounting for sales-type and direct financing leases, and requires additional disclosures to enable users of financial statements to understand the amount, timing, and uncertainty of cash flows arising from leases. Consistent with current guidance, a lessee’s recognition, measurement, and presentation of expenses and cash flows arising from a lease will continue to depend primarily on its classification. In July 2018, the FASB issued ASU No. 2018-10 and ASU No. 2018-11, which further clarifies the application of the guidance issued under ASU No. 2016-02 and provides updates to transition methods and practical expedients. ASU No. 2018-11 provides an optional transition method in addition to the existing transition method which allows entities, at the adoption date, to recognize a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption. The accounting standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, and must be applied using a modified retrospective approach. Early adoption is permitted. While the Company is continuing to assess all potential impacts of the standard, it expects that most of its lease commitments will be subject to the updated standard and recognized as lease liabilities and right-of-use assets upon adoption. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses. The standard changes how entities will measure credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. The Company will recognize an allowance for credit losses on available-for-sale securities rather than deductions in amortized cost. The standard is effective for fiscal years and interim periods beginning after December 15, 2019. Early adoption is permitted for all periods beginning after December 15, 2018. The Company is currently evaluating the impact of adopting this standard. In August 2018, the FASB issued ASU 2018-13, Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). The primary focus of the standard is to improve the effectiveness of the disclosure requirements for fair value measurements. The standard is effective for fiscal years and interim periods beginning after December 15, 2019. An entity is permitted to early adopt the removed or modified disclosures upon the issuance of the standard and may delay adoption of the additional disclosures until their effective date. The Company is currently evaluating the impact of adopting this standard. In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532, Disclosure Update and Simplification. The final rule amends certain disclosure requirements that were redundant, duplicative, overlapping, outdated or superseded. In addition, the amendments expanded the disclosure requirements on the analysis of stockholders' equity for interim financial statements. Under the amendments, an analysis of changes in each caption of stockholders' equity presented in the balance sheet must be provided in a note or separate statement. The analysis should present a reconciliation of the beginning balance to the ending balance of each period for which a statement of comprehensive income is required to be filed. The Company anticipates its first presentation of changes in stockholders' equity will be included in its Form 10-Q for the quarter ended March 31, 2019.

Investments and Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of Marketable Investments

Marketable Investments

The Company’s marketable investments have been classified and accounted for as available-for-sale. The Company’s marketable investments as of September 30, 2018 and December 31, 2017 were as follows (in thousands):



	September 30, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Commercial paper	$	12,660	$	—	$	(5	)	$	12,655
U.S. treasury	6,401		—		(37		)	6,364
U.S. agency and government sponsored securities	4,219		—		(34		)	4,185
U.S. states and municipalities	8,587		—		(23		)	8,564
Corporate bonds	114,746		60		(398		)	114,408
Total	$	146,613	$	60	$	(497	)	$	146,176



	December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Commercial paper	$	19,941	$	—	$	(8	)	$	19,933
U.S. treasury	6,402		—		(28		)	6,374
U.S. agency and government sponsored securities	4,787		—		(18		)	4,769
U.S. states and municipalities	12,510		—		(23		)	12,487
Corporate bonds	120,648		23		(280		)	120,391
Total	$	164,288	$	23	$	(357	)	$	163,954

Schedule of the Fair Value of Marketable Investments in an Unrealized Loss Position for Less than Twelve Months

The following tables present the gross unrealized losses and the fair value for those marketable investments that were in an unrealized loss position for less than twelve months or for twelve months or longer as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018
	Less than 12 months					12 months or more					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Commercial paper	$	12,655	$	(5	)	$	—	$	—		$	12,655	$	(5	)
U.S. treasury	4,371		(29		)	1,993		(8		)	6,364		(37		)
U.S. agency and government sponsored securities	4,185		(34		)	—		—			4,185		(34		)
U.S. states and municipalities	6,564		(23		)	—		—			6,564		(23		)
Corporate bonds	60,544		(244		)	13,191		(154		)	73,735		(398		)
Total	$	88,319	$	(335	)	$	15,184	$	(162	)	$	103,503	$	(497	)



	December 31, 2017
	Less than 12 months					12 months or more					Total
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
Commercial paper	$	19,933	$	(8	)	$	—	$	—		$	19,933	$	(8	)
U.S. treasury	6,374		(28		)	—		—			6,374		(28		)
U.S. agency and government sponsored securities	2,778		(9		)	1,991		(9		)	4,769		(18		)
U.S. states and municipalities	10,092		(23		)	—		—			10,092		(23		)
Corporate bonds	93,284		(188		)	10,201		(92		)	103,485		(280		)
Total	$	132,461	$	(256	)	$	12,192	$	(101	)	$	144,653	$	(357	)

Schedule of Contractual Maturities of Marketable Investments

The contractual maturities of the Company’s marketable investments as of September 30, 2018 and December 31, 2017 were as follows (in thousands):



	September 30, 2018		December 31, 2017
	Fair Value		Fair Value
Due in less than one year	$	96,143	$	104,272
Due in one to five years	50,033		59,682
Total	$	146,176	$	163,954

Schedule of Consideration Transferred in Asset Acquisition

The following table presents the components of the consideration transferred at fair value as of the Transfer Agreement Closing Date (amounts presented in thousands):



	Amount
Cash transferred	$	20,000
Anti-dilution protection at Transfer Agreement Closing Date	4,500
Carrying amount of Penumbra’s equity method investment in MVI	2,202
Fair value of the remaining non-controlling interest	3,365
Total consideration transferred	$	30,067

Schedule of Fair Value of Assets and Liabilities

The following table sets forth the Company’s financial assets measured at fair value by level within the fair value hierarchy (in thousands):



	As of September 30, 2018
	Level 1		Level 2		Level 3		Fair Value
Financial Assets
Cash equivalents:
Commercial paper	$	—	$	8,978	$	—	$	8,978
Money market funds	5,055		—		—		5,055
Marketable investments:
Commercial paper	—		12,655		—		12,655
U.S. treasury	6,364		—		—		6,364
U.S. agency and government sponsored securities	—		4,185		—		4,185
U.S. states and municipalities	—		8,564		—		8,564
Corporate bonds	—		114,408		—		114,408
Total	$	11,419	$	148,790	$	—	$	160,209
Financial Liabilities:
Contingent consideration obligations⁽¹⁾	$	—	$	—	$	2,519	$	2,519
Total	$	—	$	—	$	2,519	$	2,519



	As of December 31, 2017
	Level 1		Level 2		Level 3		Fair Value
Financial Assets
Cash equivalents:
Commercial paper	$	—	$	9,185	$	—	$	9,185
Money market funds	2,264		—		—		2,264
Marketable investments:
Commercial paper	—		19,933		—		19,933
U.S. treasury	6,374		—		—		6,374
U.S. agency and government sponsored securities	—		4,769		—		4,769
U.S. states and municipalities	—		12,487		—		12,487
Corporate bonds	—		120,391		—		120,391
Total	$	8,638	$	166,765	$	—	$	175,403
Financial Liabilities:
Contingent consideration obligations⁽¹⁾	$	—	$	—	$	4,675	$	4,675
Total	$	—	$	—	$	4,675	$	4,675

⁽¹⁾More information on the contingent consideration obligations and the changes in fair value are presented below.

Fair Value Inputs, Liabilities, Quantitative Information [Table Text Block]

In addition to the revenue generated during the earn-out and milestone periods, the following table presents certain quantitative information about unobservable inputs used in the Level 3 fair value measurement of the Company’s contingent consideration liability:



	Fair Value at September 30, 2018 (in thousands)		Valuation Method	Unobservable Inputs	Input (range where applicable)
Crossmed: Revenue-based milestones	$	2,519	Monte Carlo Simulation	Earn-out period over which revenue-based milestone payments are made	2018 - 2019
				Risk-adjusted discount rate	15%
				Revenue volatilities for each type of revenue-based milestone	8.9% and 14.8%

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]

The following table summarizes the changes in fair value of the contingent consideration obligation for the nine months ended September 30, 2018 (in thousands):



Fair Value of Contingent Consideration Obligation	Crossmed⁽¹⁾
Balance at December 31, 2017	$	4,675
Additional contingent consideration liabilities	—
Payments of contingent consideration liabilities	(3,017		)
Changes in fair value	851
Foreign currency remeasurement	10
Balance at September 30, 2018	$	2,519

⁽¹⁾During the three and nine months ended September 30, 2018, the fair value of the contingent consideration obligation related to the acquisition of Crossmed S.p.A. (“Crossmed”) increased by $0.1 million and $0.9 million, respectively, which was recorded in sales, general and administrative expense in the condensed consolidated statements of operations. The fair value of the contingent consideration increased as a result of updates to the underlying forecasts based on actual results to date and changes in estimates.

Balance Sheet Components (Tables)

9 Months Ended

Sep. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Inventories

The following table shows the components of inventories as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018		December 31, 2017
Raw materials	$	16,930	$	13,529
Work in process	9,751		6,073
Finished goods	83,025		75,299
Inventories	$	109,706	$	94,901

Schedule of Accrued Liabilities

The following table shows the components of accrued liabilities as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018		December 31, 2017
Payroll and employee-related cost	$	32,088	$	22,001
Sales return provision	3,000		3,035
Preclinical and clinical trial cost	1,112		1,514
Royalty	819		1,115
Product warranty	1,808		1,088
Leasehold improvement expenditures	860		1,012
Acquisition-related costs⁽¹⁾	3,711		4,752
Other accrued liabilities	12,785		10,308
Total accrued liabilities	$	56,183	$	44,825

⁽¹⁾Acquisition-related costs consist of the current portion of contingent liabilities related to (1) the cash milestone payments and working capital adjustment liabilities for the acquisition of Crossmed and (2) an anti-dilution provision for the asset acquisition of MVI. Refer to Note “5. Business Combination” for more information on the acquisition of Crossmed and Note “3. Investments and Fair Value of Financial Instruments” for more information on the MVI asset acquisition.

Schedule of Estimated Product Warranty Accrual

The following table shows the changes in the Company’s estimated product warranty accrual, included in accrued liabilities, as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018			December 31, 2017
Balance at the beginning of the period	$	1,088		$	1,254
Accruals of warranties issued	1,131			471
Settlements of warranty claims	(411		)	(637		)
Balance at the end of the period	$	1,808		$	1,088

Schedule of Other Non-Current Liabilities

The following table shows the components of other non-current liabilities as of September 30, 2018 and December 31, 2017 (in thousands):



	September 30, 2018		December 31, 2017
Deferred tax liabilities	$	3,235	$	3,299
Licensing-related cost⁽¹⁾	11,423		12,717
Asset acquisition-related costs⁽²⁾	2,500		—
Other non-current liabilities	1,997		2,462
Total other non-current liabilities	$	19,155	$	18,478

⁽¹⁾ Amount relates to the non-current liability recorded for probable future milestone payments to be made under the licensing agreement described in Note “6. Intangible Assets.” Refer therein for more information.

⁽²⁾Asset acquisition-related costs represents the non-current portion of the probable contingent liability related to an anti-dilution provision for the asset acquisition of MVI. Refer to Note “3. Investments and Fair Value of Financial Instruments” for more information on the MVI asset acquisition.

Business Combination (Tables)

9 Months Ended

Sep. 30, 2018

Business Combinations [Abstract]

Schedule of Business Acquisition Consideration Transferred

The following table summarizes the Closing Date fair value of the consideration transferred, reflecting the measurement period adjustments recorded in the fourth quarter of 2017 (in thousands):



Cash, net of working capital and financial debt adjustments	$	11,088
Fair value of contingent consideration for milestone payments	4,343
Contract purchase price	$	15,431
Consideration for settlement of pre-existing receivable due from Crossmed to Penumbra	3,273
Total value of consideration transferred	$	18,704

Schedule of Purchase Price Allocation

The following table presents the allocation of the purchase price for Crossmed, reflecting the measurement period adjustments recorded in 2017 (in thousands):



	Acquisition-Date Fair Value			Estimated Useful Life of Finite-Lived Intangible Assets
Tangible assets acquired and (liabilities) assumed:
Accounts receivable	$	4,406
Inventories	1,343
Other current and non-current assets	1,596
Property and equipment, net	829
Accounts payable	(740		)
Accrued liabilities and obligations for short-term debt and credit facilities	(1,868		)
Deferred tax liabilities	(2,472		)
Other non-current liabilities	(797		)
Intangible assets acquired:
Customer relationships	$	6,790		15 years
Other	1,750			5 years
Goodwill	7,867
Total purchase price	$	18,704

Goodwill (Tables)

9 Months Ended

Sep. 30, 2018

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of goodwill

The following table presents the changes in goodwill during the nine months ended September 30, 2018 (in thousands):



	Total Company
Balance as of December 31, 2017	$	8,178
Foreign currency translation	(255		)
Balance as of September 30, 2018	$	7,923

Intangible Assets (Tables)

9 Months Ended

Sep. 30, 2018

Intangible Assets, Net (Excluding Goodwill) [Abstract]

Schedule of indefinite-lived intangible assets

The following table presents details of the Company’s acquired finite-lived and indefinite-lived intangible assets, as of September 30, 2018 and December 31, 2017 (in thousands, except weighted-average amortization period):



As of September 30, 2018	Weighted-Average Amortization Period	Gross Carrying Amount		Accumulated Amortization			Net
Customer relationships	15.0 years	$	6,919	$	(576	)	$	6,343
Trade secrets and processes	20.0 years	5,256		(197		)	5,059
Other	5.0 years	1,784		(446		)	1,338
Total intangible assets subject to amortization	15.9 years	$	13,959	$	(1,219	)	$	12,740
Intangible assets related to licensed technology		14,544		—			14,544
Total intangible assets		$	28,503	$	(1,219	)	$	27,284



As of December 31, 2017	Weighted-Average Amortization Period	Gross Carrying Amount		Accumulated Amortization			Net
Customer relationships	15.0 years	$	7,141	$	(238	)	$	6,903
Other	5.0 years	1,841		(183		)	1,658
Total intangible assets subject to amortization	13.1 years	$	8,982	$	(421	)	$	8,561
Intangible assets related to licensed technology		15,217		—			15,217
Total intangible assets		$	24,199	$	(421	)	$	23,778

Finite-lived Intangible Assets Amortization Expense

The following table presents the amortization recorded related to the Company’s finite-lived intangible assets (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cost of revenue	$	66	$	—	$	197	$	—
Sales, general and administrative	205		258		631		258
Total	$	271	$	258	$	828	$	258

Stockholder's Equity (Tables)

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Stock Option Activity

Activity of stock options under the Penumbra, Inc. 2005 Stock Plan, the Penumbra, Inc. 2011 Equity Incentive Plan and the Amended and Restated Penumbra, Inc. 2014 Equity Incentive Plan (collectively the “Plans”) during the nine months ended September 30, 2018 is set forth below:



	Number of Shares		Weighted-Average Exercise Price
Balance at December 31, 2017	2,107,104		$	17.58
Exercised	(348,316	)	12.32
Canceled/Forfeited	(2,014	)	22.04
Balance at September 30, 2018	1,756,774		18.62

Summary of Unvested Restricted Stock and Restricted Stock Unit Activity

Activity of unvested restricted stock and restricted stock units under the Plans during the nine months ended September 30, 2018 is set forth below:



	Number of Shares		Weighted -Average Grant Date Fair Value
Unvested at December 31, 2017	742,405		$	38.86
Granted	109,021		110.33
Vested	(376,284	)	38.67
Canceled/Forfeited	(3,625	)	80.11
Unvested at September 30, 2018	471,517		55.21

Schedule of Stock-based Compensation Expense

The following table sets forth the stock-based compensation expense included in the Company’s condensed consolidated statements of operations for the three and nine months ended September 30, 2018 and 2017 (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Cost of revenue	$	260	$	316	$	677	$	817
Research and development	405		352		1,148		913
Sales, general and administrative	3,747		3,819		11,726		11,362
Total	$	4,412	$	4,487	$	13,551	$	13,092

Accumulated Other Comprehensive Income (Loss) (Tables)

9 Months Ended

Sep. 30, 2018

Equity [Abstract]

Schedule of Accumulated Other Comprehensive Income (Loss)

The following table summarizes the changes in the accumulated balances during the three and nine months ended September 30, 2018 and September 30, 2017, and includes information regarding the manner in which the reclassifications out of accumulated other comprehensive (loss) income into earnings affect the Company’s condensed consolidated statements of operations and condensed consolidated statements of comprehensive (loss) income (in thousands):



	Three Months Ended September 30, 2018									Three Months Ended September 30, 2017
	Marketable Investments			Currency Translation Adjustments			Total			Marketable Investments			Currency Translation Adjustments			Total
Balance at beginning of the period	$	(451	)	$	(210	)	$	(661	)	$	(38	)	$	(4,657	)	$	(4,695	)
Other comprehensive (loss) income before reclassifications:
Unrealized gain— marketable investments	151			—			151			54			—			54
Foreign currency translation (losses)	—			(353		)	(353		)	—			5,845			5,845
Income tax effect — (expense)	(36		)	—			(36		)	—			—			—
Net of tax	115			(353		)	(238		)	54			5,845			5,899
Amounts reclassified from accumulated other comprehensive income to earnings:
Realized gains — marketable investments	—			—			—			—			—			—
Income tax effect — (expense)	—			—			—			—			—			—
Net of tax	—			—			—			—			—			—
Net current-year other comprehensive income (loss)	115			(353		)	(238		)	54			5,845			5,899
Balance at end of the period	$	(336	)	$	(563	)	$	(899	)	$	16		$	1,188		$	1,204



	Nine Months Ended September 30, 2018									Nine Months Ended September 30, 2017
	Marketable Investments			Currency Translation Adjustments			Total			Marketable Investments			Currency Translation Adjustments			Total
Balance at beginning of the period	$	(235	)	$	1,804		$	1,569		$	(105	)	$	(4,583	)	$	(4,688	)
Other comprehensive (loss) income before reclassifications:
Unrealized (losses) gain— marketable investments	(102		)	—			(102		)	157			—			157
Foreign currency translation (losses)	—			(2,145		)	(2,145		)	—			5,771			5,771
Income tax effect — benefit (expense)	1			(222		)	(221		)	—			—			—
Net of tax	(101		)	(2,367		)	(2,468		)	157			5,771			5,928
Amounts reclassified from accumulated other comprehensive income to earnings:
Realized (losses)— marketable investments	—			—			—			(36		)	—			(36		)
Income tax effect — expense	—			—			—			—			—			—
Net of tax	—			—			—			(36		)	—			(36		)
Net current-year other comprehensive (loss) income	(101		)	(2,367		)	(2,468		)	121			5,771			5,892
Balance at end of the period	$	(336	)	$	(563	)	$	(899	)	$	16		$	1,188		$	1,204

Net Income (Loss) per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Reconciliation of the Numerator and Denominator used in the Calculation of the Basic and Diluted Earnings per Share

A reconciliation of the numerator and denominator used in the calculation of the basic and diluted (loss) income per share for the three and nine months ended September 30, 2018 and 2017 is as follows (in thousands, except share and per share amounts):



	Three Months Ended September 30,					Nine Months Ended September 30,
	2018			2017		2018			2017
Numerator:
Net (loss) income attributable to Penumbra, Inc.	$	(18,930	)	$	238	$	(58	)	$	(4,426	)
Denominator:
Weighted average shares used to compute net income (loss):
Basic	34,248,484			33,446,841		34,057,216			32,766,135
Effect of dilutive securities from stock-based benefit plans, as calculated using treasury stock method	—			2,217,431		—			—
Diluted	34,248,484			35,664,272		34,057,216			32,766,135
Net (loss) income attributable to Penumbra, Inc. per share from:
Basic	$	(0.55	)	$	0.01	$	—		$	(0.14	)
Diluted	$	(0.55	)	$	0.01	$	—		$	(0.14	)

Revenues (Tables)

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles

As required by ASC 606, the impact of adoption of the new revenue standard on the Company's condensed consolidated statements of operations and comprehensive income and condensed consolidated balance sheets was as follows (in thousands):



	As of September 30, 2018
				Adjusted Balance
	As Reported	Adjustments		Without 606 Adoption
Consolidated Balance Sheet Data:
Assets
Accounts receivable, net of doubtful accounts	80,435	(921	)	79,514
Inventories	109,706	314		110,020
Deferred taxes	32,985	198		33,183
Equity
Retained Earnings	2,403	(409	)	1,994



	Three Months Ended September 30, 2018						Nine Months Ended September 30, 2018
					Adjusted Balance						Adjusted Balance
	As Reported		Adjustments		Without 606 Adoption		As Reported		Adjustments		Without 606 Adoption
Consolidated Income Statement Data:
Revenue	111,806		(23	)	111,783		324,145		(263	)	323,882
Cost of revenue	36,794		(9	)	36,785		110,324		(97	)	110,227
Income (loss) from operations	(20,849	)	(14	)	(20,863	)	(7,521	)	(166	)	(7,687	)
Income (loss) before income taxes and equity in losses of unconsolidated investee	(19,908	)	(14	)	(19,922	)	(5,741	)	(166	)	(5,907	)
(Benefit from) provision for income taxes	1,598		(5	)	1,593		(5,288	)	(54	)	(5,342	)
Net income (loss) attributable to Penumbra, Inc.	(18,930	)	(9	)	(18,939	)	(58	)	(112	)	(170	)

Disaggregation of Revenue

The Company’s revenues disaggregated by geography, based on the destination to which the Company ships its products, for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
United States	$	72,991	$	55,652	$	210,070	$	157,559
Japan	10,131		8,499		31,427		24,483
Other International	28,684		19,760		82,648		55,671
Total	$	111,806	$	83,911	$	324,145	$	237,713

The Company’s revenues disaggregated by product category, for the three and nine months ended September 30, 2018 and 2017 was as follows (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Neuro	$	74,689	$	58,670	$	220,318	$	165,122
Peripheral Vascular	37,117		25,241		103,827		72,591
Total	$	111,806	$	83,911	$	324,145	$	237,713

Summary of Significant Accounting Policies - Additional Disclosures (Details)	9 Months Ended
	Sep. 30, 2018 segment activity
Accounting Policies [Abstract]
Number of business activities \| activity	1
Number of Operating Segments \| segment	1

Investments and Fair Value of Financial Instruments - Gains and Losses of Marketable Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 146,613	$ 164,288
Gross Unrealized Gains	60	23
Gross Unrealized Losses	(497)	(357)
Fair Value	146,176	163,954
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,660	19,941
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(5)	(8)
Fair Value	12,655	19,933
U.S. treasury
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,401	6,402
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(37)	(28)
Fair Value	6,364	6,374
U.S. agency and government sponsored securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,219	4,787
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(34)	(18)
Fair Value	4,185	4,769
U.S. states and municipalities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,587	12,510
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(23)	(23)
Fair Value	8,564	12,487
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	114,746	120,648
Gross Unrealized Gains	60	23
Gross Unrealized Losses	(398)	(280)
Fair Value	$ 114,408	$ 120,391

Investments and Fair Value of Financial Instruments - Marketable Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months: Fair Value	$ 88,319	$ 132,461
Less than 12 months: Gross Unrealized Losses	(335)	(256)
12 Months of more: Fair Value	15,184	12,192
12 months or more: Gross Unrealized Losses	(162)	(101)
Total: Fair Value	103,503	144,653
Total: Gross Unrealized Losses	(497)	(357)
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months: Fair Value	12,655	19,933
Less than 12 months: Gross Unrealized Losses	(5)	(8)
12 Months of more: Fair Value	0	0
12 months or more: Gross Unrealized Losses	0	0
Total: Fair Value	12,655	19,933
Total: Gross Unrealized Losses	(5)	(8)
U.S. treasury
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months: Fair Value	4,371	6,374
Less than 12 months: Gross Unrealized Losses	(29)	(28)
12 Months of more: Fair Value	1,993	0
12 months or more: Gross Unrealized Losses	(8)	0
Total: Fair Value	6,364	6,374
Total: Gross Unrealized Losses	(37)	(28)
U.S. agency and government sponsored securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months: Fair Value	4,185	2,778
Less than 12 months: Gross Unrealized Losses	(34)	(9)
12 Months of more: Fair Value	0	1,991
12 months or more: Gross Unrealized Losses	0	(9)
Total: Fair Value	4,185	4,769
Total: Gross Unrealized Losses	(34)	(18)
U.S. states and municipalities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months: Fair Value	6,564	10,092
Less than 12 months: Gross Unrealized Losses	(23)	(23)
12 Months of more: Fair Value	0	0
12 months or more: Gross Unrealized Losses	0	0
Total: Fair Value	6,564	10,092
Total: Gross Unrealized Losses	(23)	(23)
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months: Fair Value	60,544	93,284
Less than 12 months: Gross Unrealized Losses	(244)	(188)
12 Months of more: Fair Value	13,191	10,201
12 months or more: Gross Unrealized Losses	(154)	(92)
Total: Fair Value	73,735	103,485
Total: Gross Unrealized Losses	$ (398)	$ (280)

Investments and Fair Value of Financial Instruments - Contractual Maturities of Marketable Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Due in less than one year	$ 96,143	$ 104,272
Due in one to five years	50,033	59,682
Total	$ 146,176	$ 163,954

Investments and Fair Value of Financial Instruments - Non-Marketable Equity Investments (Details) - USD ($)		2 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended
	Aug. 31, 2018	Aug. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Aug. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Revenue			$ 111,806,000	$ 83,911,000		$ 324,145,000	$ 237,713,000
Net loss from equity investments			$ 920,000	545,000		$ 3,101,000	703,000
MVI Health Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method ownership percentage			50.00%			50.00%
Carrying value of investment								$ 3,900,000
Revenue						$ 0
Equity method investment, net income (loss)		$ 1,800,000		$ 1,100,000	$ 6,200,000		$ 1,400,000
MVI Health Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Asset acquisition, additional interest acquired, percentage	40.00%	40.00%			40.00%
Cash transferred	$ 20,000,000
Asset acquisition, ownership percentage	90.00%	90.00%			90.00%
Remaining equity interest	10.00%	10.00%			10.00%
Carrying value of investment	$ 2,202,000	$ 2,202,000			$ 2,202,000

Investments and Fair Value of Financial Instruments - Impact of Transfer Agreement on Non-Marketable Equity Investments (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Aug. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule of Asset Acquisition [Line Items]
Acquired in-process research and development		$ 30,835	$ 0	$ 30,835	$ 0
MVI Health Inc. [Member]
Schedule of Asset Acquisition [Line Items]
Carrying value of investment						$ 3,900
MVI Health Inc. [Member]
Schedule of Asset Acquisition [Line Items]
Carrying value of investment	$ 2,202
Cash transferred	20,000
Anti-dilution protection at Transfer Agreement Closing Date	4,500
Fair value of the remaining non-controlling interest	3,365
Contingent Liability Accrual	4,500
Acquired in-process research and development		30,835
Asset Acquisition, Consideration Transfered, Total	$ 30,067
Contingent Liability Accrual, Current		2,000		2,000
Contingent Liability Accrual, Noncurrent		$ 2,500		$ 2,500

Investments and Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Licensing-related cost, Noncurrent	$ 11,423	$ 12,717
Recurring
Financial Assets
Total	160,209	175,403
Financial Liabilities Fair Value Disclosure	2,519	4,675
Recurring \| Commercial paper
Financial Assets
Marketable investments	12,655	19,933
Recurring \| U.S. treasury
Financial Assets
Marketable investments	6,364	6,374
Recurring \| U.S. agency and government sponsored securities
Financial Assets
Marketable investments	4,185	4,769
Recurring \| U.S. states and municipalities
Financial Assets
Marketable investments	8,564	12,487
Recurring \| Corporate bonds
Financial Assets
Marketable investments	114,408	120,391
Recurring \| Commercial paper
Financial Assets
Cash equivalents	8,978	9,185
Recurring \| Money market funds
Financial Assets
Cash equivalents	5,055	2,264
Recurring \| Level 1
Financial Assets
Total	11,419	8,638
Financial Liabilities Fair Value Disclosure	0	0
Recurring \| Level 1 \| Commercial paper
Financial Assets
Marketable investments	0	0
Recurring \| Level 1 \| U.S. treasury
Financial Assets
Marketable investments	6,364	6,374
Recurring \| Level 1 \| U.S. agency and government sponsored securities
Financial Assets
Marketable investments	0	0
Recurring \| Level 1 \| U.S. states and municipalities
Financial Assets
Marketable investments	0	0
Recurring \| Level 1 \| Corporate bonds
Financial Assets
Marketable investments	0	0
Recurring \| Level 1 \| Commercial paper
Financial Assets
Cash equivalents	0	0
Recurring \| Level 1 \| Money market funds
Financial Assets
Cash equivalents	5,055	2,264
Recurring \| Level 2
Financial Assets
Total	148,790	166,765
Financial Liabilities Fair Value Disclosure	0	0
Recurring \| Level 2 \| Commercial paper
Financial Assets
Marketable investments	12,655	19,933
Recurring \| Level 2 \| U.S. treasury
Financial Assets
Marketable investments	0	0
Recurring \| Level 2 \| U.S. agency and government sponsored securities
Financial Assets
Marketable investments	4,185	4,769
Recurring \| Level 2 \| U.S. states and municipalities
Financial Assets
Marketable investments	8,564	12,487
Recurring \| Level 2 \| Corporate bonds
Financial Assets
Marketable investments	114,408	120,391
Recurring \| Level 2 \| Commercial paper
Financial Assets
Cash equivalents	8,978	9,185
Recurring \| Level 2 \| Money market funds
Financial Assets
Cash equivalents	0	0
Recurring \| Fair Value, Inputs, Level 3
Financial Assets
Total	0	0
Financial Liabilities Fair Value Disclosure	2,519	4,675
Recurring \| Fair Value, Inputs, Level 3 \| Commercial paper
Financial Assets
Marketable investments	0	0
Recurring \| Fair Value, Inputs, Level 3 \| U.S. treasury
Financial Assets
Marketable investments	0	0
Recurring \| Fair Value, Inputs, Level 3 \| U.S. agency and government sponsored securities
Financial Assets
Marketable investments	0	0
Recurring \| Fair Value, Inputs, Level 3 \| U.S. states and municipalities
Financial Assets
Marketable investments	0	0
Recurring \| Fair Value, Inputs, Level 3 \| Corporate bonds
Financial Assets
Marketable investments	0	0
Recurring \| Fair Value, Inputs, Level 3 \| Commercial paper
Financial Assets
Cash equivalents	0	0
Recurring \| Fair Value, Inputs, Level 3 \| Money market funds
Financial Assets
Cash equivalents	0	0
Contingent Consideration Liability \| Recurring
Financial Assets
Financial Liabilities Fair Value Disclosure	2,519	4,675
Contingent Consideration Liability \| Recurring \| Level 1
Financial Assets
Financial Liabilities Fair Value Disclosure	0	0
Contingent Consideration Liability \| Recurring \| Level 2
Financial Assets
Financial Liabilities Fair Value Disclosure	0	0
Contingent Consideration Liability \| Recurring \| Fair Value, Inputs, Level 3
Financial Assets
Financial Liabilities Fair Value Disclosure	$ 2,519	$ 4,675

Investments and Fair Value of Financial Instruments - Quantitative Information On Unobservable Inputs (Details) - Monte Carlo Simulation - Fair Value, Inputs, Level 3 $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 2,519
fair value inputs, risk-adjusted discount rate	15.00%
Minimum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Revenue volatilities for each type of revenue-based milestone (as a percent)	8.90%
Maximum
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Revenue volatilities for each type of revenue-based milestone (as a percent)	14.80%

Investments and Fair Value of Financial Instruments - Contingent Consideration (Details) - Crossmed(1) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
December 31, 2017		$ 4,675
Payments of contingent consideration liabilities		(3,017)
Changes in fair value	$ 100	851
Foreign currency remeasurement		10
September 30, 2018	$ 2,519	$ 2,519

Balance Sheet Components - Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Raw materials	$ 16,930	$ 13,529
Work in process	9,751	6,073
Finished goods	83,025	75,299
Inventories	$ 109,706	$ 94,901

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued Capital Expenditures And Leasehold Improvements, Current	$ 860	$ 1,012
Payroll and employee-related cost	32,088	22,001
Sales return provision	3,000	3,035
Preclinical and clinical trial cost	1,112	1,514
Royalty	819	1,115
Product warranty	1,808	1,088
Acquisition-related costs(1)	3,711	4,752
Other accrued liabilities	12,785	10,308
Total accrued liabilities	$ 56,183	$ 44,825

Balance Sheet Components - Product Warranty (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Product Warranty, Increase (Decrease) [Roll Forward]
Balance at the beginning of the period	$ 1,088	$ 1,254
Accruals of warranties issued	1,131	471
Settlements of warranty claims	(411)	(637)
Balance at the end of the period	$ 1,808	$ 1,088

Balance Sheet Components - Other Non-Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred tax liabilities	$ 3,235	$ 3,299
Licensing-related cost, Noncurrent	11,423	12,717
Acquisition-related costs	2,500	0
Other Accrued Liabilities, Noncurrent	1,997	2,462
Total other non-current liabilities	$ 19,155	$ 18,478

Business Combination - Narrative (Details) $ in Thousands, € in Millions			3 Months Ended		9 Months Ended
	Jul. 03, 2017 EUR (€)	Jul. 03, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)
Business Acquisition [Line Items]
Number of Operating Segments \| segment					1
Payment of acquisition-related obligations					$ 4,431	$ 0
Revenue			$ 111,806	$ 83,911	324,145	$ 237,713
Crossmed(1)
Business Acquisition [Line Items]
Payments to acquire business	€ 8.2	$ 9,400
Contingent Consideration Arrangements, Range of Outcomes, Maximum Unlimited				0
Payment of acquisition-related obligations					4,400
Contingent consideration for milestone payments		4,343
Deferred Tax Liabilities, Net		$ 2,472	2,500		2,500
Current Liabilities \| Crossmed(1)
Business Acquisition [Line Items]
Contingent consideration for milestone payments			$ 1,300		1,300
2017 Milestone Achievement Payment \| Crossmed(1)
Business Acquisition [Line Items]
Payment of acquisition-related obligations					$ 3,000

Business Combination - Consideration Transferred (Details) - USD ($) $ in Thousands		9 Months Ended
	Jul. 03, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Change in fair value of contingent consideration		$ 852	$ 0
Crossmed(1)
Business Acquisition [Line Items]
Purchase Consideration To Acquire Businesses Net Of Working Capital Adjustments Excluding Contingent Consideration	$ 11,088
Fair value of contingent consideration for milestone payments	4,343
Contract purchase price	15,431
Consideration for settlement of pre-existing receivable due from Crossmed to Penumbra	3,273
Total value of consideration transferred	$ 18,704
Noncurrent Liabilities \| Crossmed(1)
Business Acquisition [Line Items]
Fair value of contingent consideration for milestone payments		1,200
Current Liabilities \| Crossmed(1)
Business Acquisition [Line Items]
Fair value of contingent consideration for milestone payments		$ 1,300

Business Combination - Purchase Price Allocation (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
	Jul. 03, 2017	Sep. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Estimated Useful Life of Finite-Lived Intangible Assets		15 years 10 months 24 days	13 years 1 month 6 days
Goodwill		$ 7,923	$ 8,178
Crossmed(1)
Business Acquisition [Line Items]
Accounts receivable	$ 4,406
Inventories	1,343
Other current and non-current assets	1,596
Property and equipment, net	829
Accounts payable	(740)
Accrued liabilities and obligations for short-term debt and credit facilities	(1,868)
Deferred Tax Liabilities, Net	(2,472)	$ (2,500)
Other non-current liabilities	(797)
Goodwill	7,867
Total purchase price	18,704
Customer relationships
Business Acquisition [Line Items]
Estimated Useful Life of Finite-Lived Intangible Assets		15 years	15 years
Customer relationships \| Crossmed(1)
Business Acquisition [Line Items]
Finite-lived intangible assets acquired	$ 6,790
Estimated Useful Life of Finite-Lived Intangible Assets	15 years
Other
Business Acquisition [Line Items]
Estimated Useful Life of Finite-Lived Intangible Assets		5 years	5 years
Other \| Crossmed(1)
Business Acquisition [Line Items]
Finite-lived intangible assets acquired	$ 1,750
Estimated Useful Life of Finite-Lived Intangible Assets	5 years

Goodwill (Details) - USD ($)	3 Months Ended	9 Months Ended
Goodwill (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2018
Goodwill [Roll Forward]
Goodwill		$ 8,178,000
Foreign currency translation		(255,000)
Goodwill	$ 7,923,000	$ 7,923,000
Impairment loss	$ 0

Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period			15 years 10 months 24 days		13 years 1 month 6 days
Finite lived intangible assets: gross carrying amount	$ 13,959		$ 13,959		$ 8,982
Accumulated amortization	(1,219)		(1,219)		(421)
Finite lived intangible assets: net	12,740		12,740		8,561
Indefinite-lived intangible assets	14,544		14,544		15,217
Total intangible assets, gross	28,503		28,503		24,199
Total intangible assets, net	27,284		27,284		23,778
Total amortization of finite lived intangible assets	271	$ 258	828	$ 258
Acquisition of intangible assets from a licensing agreement		2,500	0	2,500
Licensing-related cost, Noncurrent	11,423		$ 11,423		$ 12,717
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period			15 years		15 years
Finite lived intangible assets: gross carrying amount	6,919		$ 6,919		$ 7,141
Accumulated amortization	(576)		(576)		(238)
Finite lived intangible assets: net	6,343		$ 6,343		$ 6,903
Trade secrets and processes
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period			20 years
Finite lived intangible assets: gross carrying amount	5,256		$ 5,256
Accumulated amortization	(197)		(197)
Finite lived intangible assets: net	5,059		$ 5,059
Other
Finite-Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period			5 years		5 years
Finite lived intangible assets: gross carrying amount	1,784		$ 1,784		$ 1,841
Accumulated amortization	(446)		(446)		(183)
Finite lived intangible assets: net	1,338		1,338		$ 1,658
Technology Licensing Agreement
Finite-Lived Intangible Assets [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)	300		(700)
Contingent Liability Accrual	12,000		12,000
Cost of revenue
Finite-Lived Intangible Assets [Line Items]
Total amortization of finite lived intangible assets	66	0	197	0
Sales, general and administrative
Finite-Lived Intangible Assets [Line Items]
Total amortization of finite lived intangible assets	205	$ 258	631	$ 258
Accrued Liabilities \| Technology Licensing Agreement
Finite-Lived Intangible Assets [Line Items]
Contingent Liability Accrual, Current	600		600
Noncurrent Liabilities \| Technology Licensing Agreement
Finite-Lived Intangible Assets [Line Items]
Contingent Liability Accrual, Noncurrent	$ 11,400		$ 11,400

Commitments and Contingencies - Lease and Purchase Commitments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Leases [Line Items]
Rent expense	$ 1.4	$ 1.4	$ 4.3	$ 4.3
Headquarters, Additional Lease [Member] \| Minimum
Operating Leases [Line Items]
Lessor, Operating Lease, Renewal Term			5 years
Headquarters, Additional Lease [Member] \| Maximum
Operating Leases [Line Items]
Lessor, Operating Lease, Renewal Term			15 years

Commitments and Contingencies - Royalty Obligations (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Other Commitments [Line Items]
Common shares issued as consideration in connection with a buyout agreement (Notes 6, 8 and 9)				$ 5,256,000	$ 0
Finite lived intangible assets: gross carrying amount	$ 13,959,000			13,959,000		$ 8,982,000
Cost of revenue
Other Commitments [Line Items]
Royalty expense	900,000		$ 1,000,000	2,400,000	$ 3,000,000
Royalty Agreement, March 2005
Other Commitments [Line Items]
Minimum annual royalty payments	100,000			$ 100,000		$ 100,000
Term of agreement				15 years
Royalty Agreement, April 2012
Other Commitments [Line Items]
Term of agreement				15 years
Royalty as a percent of sales				5.00%
Royalty Agreement, November 2013, Less than $5 Million in Sales
Other Commitments [Line Items]
Royalty as a percent of sales				3.00%
Royalty Agreement, November 2013, Greater than $5 Million in Sales
Other Commitments [Line Items]
Royalty as a percent of sales				1.00%
Royalty threshold				$ 5,000,000
Royalty Agreement, April 2015
Other Commitments [Line Items]
Royalty as a percent of sales				2.00%
Common shares issued as consideration in connection with a buyout agreement (Notes 6, 8 and 9)		$ 5,300,000
Trade secrets and processes
Other Commitments [Line Items]
Finite lived intangible assets: gross carrying amount	$ 5,256,000			$ 5,256,000

Stockholder's Equity - Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Subsidiary, Sale of Stock [Line Items]
Common shares issued as consideration in connection with a buyout agreement (Notes 6, 8 and 9)			$ 5,256	$ 0
Underwritten Public Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued and sold (in shares)	1,495,000
Public offering price (in USD per share)	$ 76.00
Net cash proceeds from shares issued and sold	$ 106,300
Underwriting discounts and commissions	6,800
Other offering expenses	$ 500
Restricted Stock Units (RSUs)
Subsidiary, Sale of Stock [Line Items]
Granted (in shares)		53,256
Royalty Agreement, April 2015
Subsidiary, Sale of Stock [Line Items]
Common shares issued as consideration in connection with a buyout agreement (Notes 6, 8 and 9)		$ 5,300

Stockholder's Equity - Stock Option Activity (Details)	9 Months Ended
Stockholder's Equity - Stock Option Activity (Details)	Sep. 30, 2018 $ / shares shares
Number of Shares
Beginning balance (in shares) \| shares	2,107,104
Options exercised (in shares) \| shares	(348,316)
Options cancelled (in shares) \| shares	(2,014)
Ending balance (in shares) \| shares	1,756,774
Weighted-Average Exercise Price
Beginning balance (in dollars per share) \| $ / shares	$ 17.58
Options exercised (in dollars per share) \| $ / shares	12.32
Options cancelled (in dollars per share) \| $ / shares	22.04
Ending balance (in dollars per share) \| $ / shares	$ 18.62

Stockholder's Equity - Restricted Stock and Restricted Stock Units Activity (Details) - Restricted stock and restricted stock units	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Number of Shares
Unvested beginning balance (in shares)	742,405
Granted (in shares)	109,021
Vested (in shares)	(376,284)
Canceled/Forfeited (in shares)	(3,625)
Unvested and expected to vest ending balance (in shares)	471,517
Weighted -Average Grant Date Fair Value
Unvested beginning balance (in dollars per share) \| $ / shares	$ 38.86
Granted (in dollars per share) \| $ / shares	110.33
Vested (in dollars per share) \| $ / shares	38.67
Canceled/Forfeited (in dollars per share) \| $ / shares	80.11
Unvested and expected to vest ending balance (in dollars per share) \| $ / shares	$ 55.21
Restricted stock and RSUs expected to vest (shares)	460,432

Stockholder's Equity - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 4,412	$ 4,487	$ 13,551	$ 13,092
Unrecognized compensation cost related to unvested share-based compensation arrangements	23,700		$ 23,700
Unrecognized compensation cost, expected recognition period			2 years 2 months 1 day
Share-based compensation expense, capitalized in inventory			$ 400		$ 200
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	260	316	677	817
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	405	352	1,148	913
Sales, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,747	$ 3,819	$ 11,726	$ 11,362

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			$ 400,408
Amounts reclassified from accumulated other comprehensive income to earnings:
Total other comprehensive (loss) income, net of tax	$ (238)	$ 5,899	(2,468)	$ 5,892
Ending balance	409,419		409,419
Marketable Investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(451)	(38)	(235)	(105)
Other comprehensive (loss) income before reclassifications:
Other comprehensive income before reclassifications	151	54	(102)	157
Income tax effect — (expense) benefit	(36)	0	1	0
Net of tax	115	54	(101)	157
Amounts reclassified from accumulated other comprehensive income to earnings:
Realized gains — marketable investments	0	0	0	(36)
Income tax effect — (expense)	0	0	0	0
Net of tax	0	0	0	(36)
Total other comprehensive (loss) income, net of tax	115	54	(101)	121
Ending balance	(336)	16	(336)	16
Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(210)	(4,657)	1,804	(4,583)
Other comprehensive (loss) income before reclassifications:
Other comprehensive income before reclassifications	(353)	5,845	(2,145)	5,771
Income tax effect — (expense) benefit	0	0	(222)	0
Net of tax	(353)	5,845	(2,367)	5,771
Amounts reclassified from accumulated other comprehensive income to earnings:
Realized gains — marketable investments	0	0	0	0
Income tax effect — (expense)	0	0	0	0
Net of tax	0	0	0	0
Total other comprehensive (loss) income, net of tax	(353)	5,845	(2,367)	5,771
Ending balance	(563)	1,188	(563)	1,188
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(661)	(4,695)	1,569	(4,688)
Other comprehensive (loss) income before reclassifications:
Income tax effect — (expense) benefit	(36)	0	(221)	0
Net of tax	(238)	5,899	(2,468)	5,928
Amounts reclassified from accumulated other comprehensive income to earnings:
Realized gains — marketable investments	0	0	0	(36)
Income tax effect — (expense)	0	0	0	0
Net of tax	0	0	0	(36)
Total other comprehensive (loss) income, net of tax	(238)	5,899	(2,468)	5,892
Ending balance	$ (899)	$ 1,204	$ (899)	$ 1,204

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Contingency [Line Items]
Provision for (benefit from) income taxes	$ 1,598	$ 456	$ (5,288)	$ 2,293
Effective tax rate	(8.00%)	36.80%	92.10%	(160.30%)
Domestic Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Period	20 years

Net Income (Loss) per Share - Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net (loss) income attributable to Penumbra, Inc.	$ (18,930)	$ 238	$ (58)	$ (4,426)
Denominator:
Weighted average shares used to compute net (loss) income per share attributable to common stockholders — Basic (in shares)	34,248,484	33,446,841	34,057,216	32,766,135
Potential dilutive shares (in shares)	0	2,217,431	0	0
Weighted average shares used to compute net income attributable to common stockholders —Diluted (in shares)	34,248,484	35,664,272	34,057,216	32,766,135
Net (loss) income per share attributable to common stockholders — Basic (in dollars per share)	$ (0.55)	$ 0.01	$ 0.00	$ (0.14)
Net (loss) income per share attributable to common stockholders — Diluted (in dollars per share)	$ (0.55)	$ 0.01	$ 0.00	$ (0.14)

Net Income (Loss) per Share - Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from the computation of earnings per share (in shares)	2,260,700	0	2,260,700	3,000,000

Revenues - Initial Application Period (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Consolidated Balance Sheet Data:
Accounts receivable, net of doubtful accounts	$ 80,435		$ 80,435
Inventories	109,706		109,706			$ 94,901
Deferred taxes	32,985		32,985
Retained earnings	2,403		2,403			$ 1,996
Consolidated Income Statement Data:
Revenue	111,806	$ 83,911	324,145	$ 237,713
Cost of revenue	36,794	29,134	110,324	84,298
Income (loss) from operations	(20,849)	683	(7,521)	(2,691)
Income (loss) before income taxes and equity in losses of unconsolidated investee	(19,908)		(5,741)
(Benefit from) provision for income taxes	1,598	456	(5,288)	2,293
Net income (loss) attributable to Penumbra, Inc.	(18,930)	$ 238	(58)	$ (4,426)
As Reported
Consolidated Balance Sheet Data:
Accounts receivable, net of doubtful accounts	79,514		79,514
Inventories	110,020		110,020
Deferred taxes	33,183		33,183
Retained earnings	1,994		1,994
Consolidated Income Statement Data:
Revenue	111,783		323,882
Cost of revenue	36,785		110,227
Income (loss) from operations	(20,863)		(7,687)
Income (loss) before income taxes and equity in losses of unconsolidated investee	(19,922)		(5,907)
(Benefit from) provision for income taxes	1,593		(5,342)
Net income (loss) attributable to Penumbra, Inc.	(18,939)		(170)
Adjustments \| Accounting Standards Update 2014-09
Consolidated Balance Sheet Data:
Accounts receivable, net of doubtful accounts	(921)		(921)
Inventories	314		314
Deferred taxes	198		198
Retained earnings	(409)		(409)
Consolidated Income Statement Data:
Revenue	(23)		(263)
Cost of revenue	(9)		(97)
Income (loss) from operations	(14)		(166)
Income (loss) before income taxes and equity in losses of unconsolidated investee	(14)		(166)
(Benefit from) provision for income taxes	(5)		(54)
Net income (loss) attributable to Penumbra, Inc.	$ (9)		$ (112)
Retained Earnings \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative effect of new accounting principle					$ 300

Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 111,806	$ 83,911	$ 324,145	$ 237,713
United States
Disaggregation of Revenue [Line Items]
Revenue	72,991	55,652	210,070	157,559
Japan
Disaggregation of Revenue [Line Items]
Revenue	10,131	8,499	31,427	24,483
Other International
Disaggregation of Revenue [Line Items]
Revenue	28,684	19,760	82,648	55,671
Neuro
Disaggregation of Revenue [Line Items]
Revenue	74,689	58,670	220,318	165,122
Peripheral Vascular
Disaggregation of Revenue [Line Items]
Revenue	$ 37,117	$ 25,241	$ 103,827	$ 72,591