Karyopharm Therapeutics (KPTI) 10-Q 2 Nov 20 2020 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Oct. 28, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Registrant Name	Karyopharm Therapeutics Inc.
Trading Symbol	KPTI
Entity Central Index Key	0001503802
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		73,600,777
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity File Number	001-36167
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-3931704
Entity Address, Address Line One	85 Wells Avenue, 2nd Floor
Entity Address, City or Town	Newton
Entity Address, Postal Zip Code	02459
City Area Code	617
Local Phone Number	658-0600
Document Transition Report	false
Document Quarterly Report	true
Entity Shell Company	false
Entity Address, State or Province	MA
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 82,301	$ 128,858
Short-term investments	180,743	133,098
Accounts receivable	11,062	7,862
Inventory	2,011	346
Prepaid expenses and other current assets	8,242	7,289
Restricted cash	1,088	1,117
Total current assets	285,447	278,570
Property and equipment, net	2,357	3,046
Operating lease right-of-use assets	9,694	10,617
Long-term investments	39,371	2,016
Restricted cash	718	714
Total assets	337,587	294,963
Current liabilities:
Accounts payable	2,422	985
Accrued expenses	46,591	40,878
Deferred revenue	297	2,341
Operating lease liabilities	1,847	1,646
Other current liabilities	1,473	500
Total current liabilities	52,630	46,350
Convertible senior notes	115,802	109,857
Deferred royalty obligation	73,588	73,588
Operating lease liabilities, net of current portion	11,797	13,202
Deferred revenue, net of current portion		2,192
Total liabilities	253,817	245,189
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000 shares authorized; none issued and outstanding
Common stock, $0.0001 par value; 200,000 shares authorized; 73,528 and 65,370 shares issued and outstanding at September 30, 2020 and December 31, 2019, respectively	7	7
Additional paid-in capital	1,109,350	923,142
Accumulated other comprehensive income (loss)	603	(37)
Accumulated deficit	(1,026,190)	(873,338)
Total stockholders’ equity	83,770	49,774
Total liabilities and stockholders’ equity	$ 337,587	$ 294,963

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	73,528,000	65,370,000
Common stock, shares outstanding	73,528,000	65,370,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Total revenues	$ 21,333	$ 13,149	$ 72,985	$ 22,797
Operating expenses:
Cost of sales	438	1,013	1,653	1,013
Research and development	37,037	26,270	113,628	90,761
Selling, general and administrative	30,967	25,267	92,488	77,032
Total operating expenses	68,442	52,550	207,769	168,806
Loss from operations	(47,109)	(39,401)	(134,784)	(146,009)
Other income (expense):
Interest income	600	1,137	2,424	4,320
Interest expense	(6,801)	(3,093)	(20,068)	(9,180)
Other (expense) income, net	(141)	10	(177)	(36)
Total other expense, net	(6,342)	(1,946)	(17,821)	(4,896)
Loss before income taxes	(53,451)	(41,347)	(152,605)	(150,905)
Income tax provision	(44)	(20)	(247)	(38)
Net loss	$ (53,495)	$ (41,367)	$ (152,852)	$ (150,943)
Net loss per share—basic and diluted	$ (0.73)	$ (0.67)	$ (2.14)	$ (2.46)
Weighted-average number of common shares outstanding used in net loss per share—basic and diluted	73,466	62,093	71,479	61,297
Product revenue
Revenues:
Total revenues	$ 21,330	$ 12,821	$ 55,992	$ 12,821
License and other revenue
Revenues:
Total revenues	$ 3	$ 328	$ 16,993	$ 9,976

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (53,495)	$ (41,367)	$ (152,852)	$ (150,943)
Comprehensive income (loss)
Unrealized (loss) gain on investments	(319)	(59)	640	250
Foreign currency translation adjustment	31	(32)		(36)
Comprehensive loss	$ (53,783)	$ (41,458)	$ (152,212)	$ (150,729)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net loss	$ (152,852)	$ (150,943)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	715	730
Net amortization of premiums and discounts on investments	710	(1,242)
Amortization of debt discount and issuance costs	5,945	5,298
Stock-based compensation expense	18,093	11,742
Changes in operating assets and liabilities:
Accounts receivable	(3,200)	(7,928)
Inventory	(1,665)	(100)
Prepaid expenses and other current assets	(953)	1,108
Operating lease right-of-use assets	924	807
Accounts payable	1,437	(1,215)
Accrued expenses and other liabilities	6,686	569
Deferred revenue	(4,236)	(9,362)
Operating lease liabilities	(1,204)	(797)
Net cash used in operating activities	(129,600)	(151,333)
Investing activities
Purchases of property and equipment	(26)	(156)
Proceeds from maturities of investments	162,855	202,454
Purchases of investments	(247,911)	(90,329)
Net cash (used in) provided by investing activities	(85,082)	111,969
Financing activities
Proceeds from issuance of common stock, net of issuance costs	161,802	14,563
Proceeds from the exercise of stock options and shares issued under employee stock purchase plan	6,313	1,124
Proceeds from deferred royalty obligation, net		73,682
Net cash provided by financing activities	168,115	89,369
Effect of exchange rate on cash, cash equivalents and restricted cash	(15)	(26)
Net (decrease) increase in cash, cash equivalents and restricted cash	(46,582)	49,979
Cash, cash equivalents and restricted cash at beginning of period	130,689	118,737
Cash, cash equivalents and restricted cash at end of period	84,107	168,716
Reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets
Cash and cash equivalents	82,301	168,004
Short-term restricted cash	1,088
Long-term restricted cash	718	712
Total cash, cash equivalents and restricted cash	84,107	168,716
Supplemental disclosures:
Operating lease right-of-use assets obtained in exchange for operating lease liabilities		11,711
Cash paid for amounts included in the measurement of operating lease liabilities	2,388	$ 2,096
Cash paid for interest on deferred royalty obligation	$ 4,521

Condensed Consolidated Statem_4

Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2018	$ 183,170	$ 6	$ 857,156	$ (244)	$ (673,748)
Beginning balance,Shares at Dec. 31, 2018		60,829,000
Vesting of restricted stock (in shares)		10,000
Exercise of stock options and shares issued under the employee stock purchase plan	1,124		1,124
Exercise of stock options and shares issued under the employee stock purchase plan, (shares)		232,000
Issuance of common stock, net of issuance costs	14,563		14,563
Issuance of common stock (in Shares)		1,634,000
Stock-based compensation expense	11,742		11,742
Unrealized gain (loss) on investments	250			250
Foreign currency translation adjustment	(36)			(36)
Net loss	(150,943)				(150,943)
Ending balance at Sep. 30, 2019	59,870	$ 6	884,585	(30)	(824,691)
Ending balance,Shares at Sep. 30, 2019		62,705,000
Beginning balance at Jun. 30, 2019	82,469	$ 6	865,726	61	(783,324)
Beginning balance,Shares at Jun. 30, 2019		60,965,000
Vesting of restricted stock (in shares)		5,000
Exercise of stock options and shares issued under the employee stock purchase plan	577		577
Exercise of stock options and shares issued under the employee stock purchase plan, (shares)		101,000
Issuance of common stock, net of issuance costs	14,563		14,563
Issuance of common stock (in Shares)		1,634,000
Stock-based compensation expense	3,719		3,719
Unrealized gain (loss) on investments	(59)			(59)
Foreign currency translation adjustment	(32)			(32)
Net loss	(41,367)				(41,367)
Ending balance at Sep. 30, 2019	59,870	$ 6	884,585	(30)	(824,691)
Ending balance,Shares at Sep. 30, 2019		62,705,000
Beginning balance at Dec. 31, 2019	49,774	$ 7	923,142	(37)	(873,338)
Beginning balance,Shares at Dec. 31, 2019		65,370,000
Vesting of restricted stock (in shares)		199,000
Exercise of stock options and shares issued under the employee stock purchase plan	6,313		6,313
Exercise of stock options and shares issued under the employee stock purchase plan, (shares)		771,000
Issuance of common stock, net of issuance costs	161,802		161,802
Issuance of common stock (in Shares)		7,188,000
Stock-based compensation expense	18,093		18,093
Unrealized gain (loss) on investments	640			640
Net loss	(152,852)				(152,852)
Ending balance at Sep. 30, 2020	83,770	$ 7	1,109,350	603	(1,026,190)
Ending balance,Shares at Sep. 30, 2020		73,528,000
Beginning balance at Jun. 30, 2020	129,799	$ 7	1,101,596	891	(972,695)
Beginning balance,Shares at Jun. 30, 2020		73,366,000
Vesting of restricted stock (in shares)		10,000
Exercise of stock options and shares issued under the employee stock purchase plan	1,241		1,241
Exercise of stock options and shares issued under the employee stock purchase plan, (shares)		152,000
Stock-based compensation expense	6,513		6,513
Unrealized gain (loss) on investments	(319)			(319)
Foreign currency translation adjustment	31			31
Net loss	(53,495)				(53,495)
Ending balance at Sep. 30, 2020	$ 83,770	$ 7	$ 1,109,350	$ 603	$ (1,026,190)
Ending balance,Shares at Sep. 30, 2020		73,528,000

Nature of Business and Basis of

Nature of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Nature of Business and Basis of Presentation	1. Nature of Business and Basis of Presentation Nature of Business Karyopharm Therapeutics Inc., a Delaware corporation (collectively with its subsidiaries, the “Company,” “we,” “us,” or “our”), is a commercial-stage pharmaceutical company pioneering novel cancer therapies and dedicated to the discovery, development and commercialization of novel, first-in-class drugs directed against nuclear export and related targets for the treatment of cancer and other major diseases. We were incorporated in Delaware on December 22, 2008 and have a principal place of business in Newton, Massachusetts. Our S elective I nhibitor of N uclear E xport SINE ® ® Basis of Presentation The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments (including those which are normal and recurring) considered necessary for a fair presentation of the interim financial information have been included. When preparing financial statements in conformity with GAAP, we must make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, expenses and related disclosures at the date of the financial statements. Actual results could differ from those estimates. Additionally, operating results for the three and nine months ended September 30, 2020 are not necessarily indicative of the results that may be expected for any other interim period or for the fiscal year ending December 31, 2020. For further information, refer to the financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2019 as filed with the Securities and Exchange Commission (“SEC”) on February 26, 2020 (“Annual Report”). Basis of Consolidation The condensed consolidated financial statements at September 30, 2020 include the accounts of Karyopharm Therapeutics Inc. and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The significant accounting policies used in preparation of these condensed consolidated financial statements on Form 10-Q are consistent with those discussed in Note 2, “ Summary of Significant Accounting Policies

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2020
Accounting Changes And Error Corrections [Abstract]
Recent Accounting Pronouncements	2. Recent Accounting Pronouncements and CARES Act Provisions Recently Adopted Accounting Standards In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement - Disclosure Framework-Changes to the Disclosure Requirement for Fair Value Measurement (“ASU 2018-13”). The amendments in ASU 2018-13 modify the disclosure requirements on fair value measurements in Accounting Standards Codification (“ASC”) 820, Fair Value Measurement , based on the concepts in the FASB Concepts Statement, including the consideration of costs and benefits. The amendments under ASU 2018-13 are effective for interim and annual fiscal periods beginning after December 15, 2019, with early adoption permitted. We adopted this guidance effective January 1, 2020. The adoption of this standard did not have a material impact on our condensed consolidated financial statements. Recently Issued Accounting Standard In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging— Contracts in Entity’s Own Equity (Subtopic 815-40) the changes are a trade-off between simplifications in the accounting model, including no separation of an “equity” component to impute a market interest rate, as well as simpler analysis of embedded equity features, and a potentially adverse impact to diluted earnings per share (“EPS”) by requiring the use of the if-converted method. CARES Act In March 2020, the Coronavirus Aid, Relief, and Economic Security (“CARES”) Act was signed into law and provides an estimated $2.2 trillion to fight the COVID-19 pandemic and stimulate the U.S. economy. The business tax provisions of the CARES Act include temporary changes to income and non-income-based tax laws. Some of the key income tax provisions include (1) eliminating 80% of taxable income limitations by allowing corporate entities to fully utilize net operating loss (“NOL”) carryforwards to offset taxable income in 2020, 2019 or 2018 and reinstating it for tax years after 2020; (2) allowing NOLs generated in 2020, 2019 or 2018 to be carried back five years; (3) increasing the net interest expense deduction limit to 50% of adjusted taxable income from 30% for the 2020 and 2019 tax years; (4) allowing taxpayers with alternative minimum tax credits to claim a refund for the entire amount of the credit instead of recovering the credit through refunds over a period of years, as required by the 2017 Tax Cut and Jobs Act; and (5) allowing entities to deduct more of their charitable cash contributions made during calendar year 2020 by increasing the taxable income limitation to 25% from 10%. Companies are required to account for these provisions in the period that includes the March 2020 enactment date (i.e., the first quarter for calendar year-end entities). We have assessed the impact of these provisions and they are not material to our condensed consolidated financial statements or related disclosures. Measures not related to income-based taxes within the CARES Act include (1) allowing an employer to pay its share of Social Security payroll taxes that would otherwise be due from the date of enactment through December 31, 2020 over the following two years and (2) allowing eligible employers subject to closure due to the COVID-19 pandemic to receive a 50% credit on qualified wages against their employment taxes each quarter, with any excess credits eligible for refunds. These measures of the CARES Act also are not material to our condensed consolidated financial statements or related disclosures.

Product Revenue

Product Revenue	9 Months Ended
	Sep. 30, 2020
Product Revenue [Member]
Product Revenue	3. Product Revenue To date, our only source of product revenue has been from the U.S. sales of XPOVIO, which we began shipping to our customers in July 2019. Net product revenue, including provisions primarily consisting of distribution fees and cash discounts, as well as reserves for chargebacks, rebates and returns, were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Gross product revenue $ 25,322 $ 14,960 $ 66,440 $ 14,960 Provision for product revenue (3,992 ) (2,139 ) (10,448 ) (2,139 ) Total product revenue, net $ 21,330 $ 12,821 $ 55,992 $ 12,821 As of September 30, 2020 and December 31, 2019, net product revenue of $11.1 million and $7.9 million, respectively, were included in accounts receivable. To date, we have had no bad debt write-offs and we do not currently have credit issues with any customers. There were no credit losses associated with our accounts receivables as of September 30, 2020 and December 31, 2019.

Inventory

Inventory	9 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Inventory	4. Inventory The following table presents our inventory of XPOVIO (in thousands): September 30, 2020 December 31, 2019 Raw materials and work in process $ 1,566 $ 273 Finished goods 445 73 Total inventory $ 2,011 $ 346 As of September 30, 2020 and December 31, 2019, all of our inventory was related to XPOVIO, which was initially approved by the FDA in July 2019 and at which time we began to capitalize costs to manufacture XPOVIO. Prior to FDA approval of XPOVIO, all costs related to the manufacturing of XPOVIO and related material were charged to research and development expense in the period incurred. As of September 30, 2020 and December 31, 2019, we determined that a reserve related to XPOVIO inventory was not required.

License and Asset Purchase Agre

License and Asset Purchase Agreements	9 Months Ended
	Sep. 30, 2020
License and Asset Purchase Agreements [Member]
Product Revenue	5. License and Asset Purchase Agreements In prior periods, we entered into out-licensing and asset purchase agreements with Anivive Lifesciences, Inc. (“Anivive”), Ono Pharmaceutical Co., Ltd. (“Ono”), Biogen MA Inc. (“Biogen”), and Antengene Therapeutics Limited (“Antengene”), all of which are accounted for within the scope of ASC 606, Revenue from Contracts with Customers License and Asset Purchase Agreements In April 2020, we terminated our October 2017 license agreement with Ono for the development and commercialization of selinexor and eltanexor for all human oncology indications in Japan, South Korea, Taiwan, Hong Kong, and the countries in the Association of Southeast Asian Nations. Subsequent to termination, all rights to selinexor and eltanexor were returned to us and no further consideration was exchanged between the parties. Accordingly, we recognized $2.2 million in license and other revenue during the nine months ended September 30, 2020, which represented the deferred revenue on the contract as of the date of termination. In May 2020, we entered into an amendment to our May 2018 license agreement with Antengene (the “Original Antengene Agreement” and, as amended, the “Amended Antengene Agreement”) to expand the territory for the exclusive development and commercialization rights of selinexor, eltanexor and KPT-9274, each for the diagnosis, treatment and/or prevention of all human oncology indications, as well as verdinexor for the diagnosis, treatment and/or prevention of certain human non-oncology indications (“Antengene Licensed Compounds”). Under the terms of the Original Antengene Agreement, we received an upfront cash payment of $11.7 million. Under the terms of the Amended Antengene Agreement, Antengene now has the exclusive development and commercialization rights for selinexor, eltanexor, KPT-9274 and verdinexor in mainland China, Taiwan, Hong Kong, Macau, South Korea, Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Philippines, Singapore, Thailand, Vietnam, Australia and New Zealand (the “Antengene Territory”). Previously, Antengene’s territory covered mainland China and Macau for selinexor and eltanexor and mainland China, Taiwan, Hong Kong, Macau, South Korea, Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Philippines, Singapore, Thailand, and Vietnam for KPT-9274 and verdinexor. Furthermore, we received a one-time upfront cash payment of $ 11.7 million in June 2020 and are entitled to future milestone payments from Antengene if certain development , regulatory and commercialization goals are achieved. Finally , we are also eligible to receive tiered double-digit royalties based on future net sales of selinexor and eltanexor, and tiered single- to double-digit royalties based on future net sales of verdinexor and KPT-9274 in the Antengene T erritory. We assessed the Amended Antengene Agreement in accordance with ASC 606 and concluded that the amendment was a contract modification. We further concluded that the performance obligations under the Amended Antengene Agreement were the same performance obligations identified in the Original Antengene Agreement, as disclosed in Note 11, “License and Asset Purchase Agreements ” Based on the conclusions noted, we updated the transaction price, which includes the $1.3 million unrecognized deferred revenue from the $11.7 million upfront payment we received from Antengene under the terms of the Original Antengene Agreement, and the $11.7 million upfront payment we received from Antengene under the terms of the Amended Antengene Agreement, and allocated the total, or $13.0 million, to the remaining performance obligations based on their estimated standalone selling prices as of the effective date of the Amended Antengene Agreement. Since we had already fulfilled all of our promises under the combined performance obligations for selinexor and KPT-9274 as of the effective date of the Amended Antengene Agreement, we recognized a cumulative adjustment to license revenue of $12.7 million during the nine months ended September 30, 2020. For the remaining promises to be fulfilled under the combined performance obligation for eltanexor, we adjusted short-term deferred revenue to $0.3 million as of September 30, 2020 will recognize such revenue when initial clinical supply of eltanexor is delivered to Antengene, which we expect to be within twelve months from September 30, 2020. For the remaining promises to be fulfilled under the combined performance obligation for verdinexor, none of the transaction price was allocated thereto, as it was assessed as immaterial in comparison to the other combined performance obligations under the Amended Antengene Agreement. Finally, we also reassessed other promised goods and services within the modified contract, including customer options and material rights, ultimately concluding such promised goods and services continue to be immaterial. The future regulatory and commercial milestones, both of which represent variable consideration, were evaluated under the most likely amount method, and were not included in the transaction price at contract inception and/or through September 30, 2020, because the amounts were fully constrained as of September 30, 2020. As part of our evaluation of the constraint, we considered numerous factors, including that receipt of such amounts is outside of our control. Separately, any consideration related to sales-based milestones, as well as royalties on net sales upon commercialization of XPOVIO by Antengene, will be recognized when the related sales occur, as they were determined to relate predominantly to the intellectual property licenses granted to Antengene and, therefore, have also been excluded from the transaction price in accordance with the sales-based royalty exception, as well as our accounting policy. We will the transaction price in each reporting period, as uncertain events are resolved, or as other changes in circumstances occur. In summary, we recognized $14.9 million in license and other revenue for the nine months ended September 30, 2020, related to the license agreements with Ono and Antengene described above. As summarized in the following table, which presents changes in balance sheet accounts for our out-licensing and asset purchase agreements, we recognized $2.3 million under the Original Antengene Agreement and $2.2 million upon termination of the license agreement with Ono during the nine months ended September 30, 2020 (in thousands): December 31, 2019 Additions Deductions September 30, 2020 Short-term Deferred Revenue Original Antengene Agreement $ 2,341 $ — $ (2,341 ) $ — Amended Antengene Agreement — 297 — 297 Total short-term deferred revenue $ 2,341 $ 297 $ (2,341 ) $ 297 Long-term Deferred Revenue Ono $ 2,192 $ — $ (2,192 ) $ — Total long-term deferred revenue $ 2,192 $ — $ (2,192 ) $ — Total deferred revenue $ 4,533 $ 297 $ (4,533 ) $ 297

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	6. Fair Value of Financial Instruments Financial instruments, including cash, restricted cash, prepaid expenses and other current assets, accounts payable and accrued expenses, are presented at amounts that approximate fair value at September 30, 2020 and December 31, 2019. We are required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. The fair value hierarchy prioritizes valuation inputs based on the observable nature of those inputs. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs: Level 1 inputs - Quoted prices in active markets for identical assets or liabilities Level 2 inputs - Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly Level 3 inputs - Unobservable inputs that reflect our own assumptions about the assumptions market participants would use in pricing the asset or liability Our cash equivalents are comprised of money market funds and U.S. government and agency securities. We measure these investments at fair value. The fair value of cash equivalents held in money market funds and U.S. treasury securities is determined based on “Level 1” inputs. Items classified as Level 2 within the valuation hierarchy consist of commercial paper, corporate debt securities, and U.S. government and agency securities. We estimate the fair values of these marketable securities by taking into consideration valuations obtained from third-party pricing sources. These pricing sources utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include market pricing based on real-time trade data for the same or similar securities, issuer credit spreads, benchmark yields, and other observable inputs. We validate the prices provided by our third-party pricing sources by understanding the models used, obtaining market values from other pricing sources and analyzing pricing data in certain instances. In certain cases where there is limited activity or less transparency around inputs to valuation, the related assets or liabilities are classified as Level 3. The embedded derivative liability associated with our deferred royalty obligation, as discussed further in Note 11, “ Long-Term Obligations Summary of Significant Accounting Policies Long-Term Obligations The following table presents information about our financial assets and liability that have been measured at fair value at September 30, 2020 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands): Description Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets Cash equivalents: Money market funds $ 29,555 $ 29,555 $ — $ — U.S. government and agency securities 8,998 8,998 — — Investments: Short-term: Corporate debt securities 134,750 — 134,750 — Commercial paper 42,974 — 42,974 — U.S. government and agency securities 3,019 — 3,019 — Long-term: Corporate debt securities (one to two-year maturity) 38,467 — 38,467 — U.S. government and agency securities (one to two-year maturity) 904 — 904 — $ 258,667 $ 38,553 $ 220,114 $ — Financial liability Embedded derivative liability $ 2,300 $ — $ — $ 2,300 The following table presents information about our financial assets and liability that have been measured at fair value at December 31, 2019 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands): Description Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets Cash equivalents: Money market funds $ 71,380 $ 71,380 $ — $ — Investments: Short-term: Corporate debt securities 89,079 — 89,079 — Commercial paper 39,022 — 39,022 — U.S. government and agency securities 4,997 — 4,997 — Long-term: Corporate debt securities (one to two-year maturity) 2,016 — 2,016 — $ 206,494 $ 71,380 $ 135,114 $ — Financial liability Embedded derivative liability $ 2,300 $ — $ — $ 2,300

Investments

Investments	9 Months Ended
	Sep. 30, 2020
Investments Debt And Equity Securities [Abstract]
Investments	7. Investments The following table summarizes our investments in corporate debt securities, commercial paper, and U.S. government and agency securities, classified as available-for-sale, as of September 30, 2020 (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Loss Fair Value Short-term: Corporate debt securities $ 134,394 $ 371 $ (15 ) $ 134,750 Commercial paper 42,969 6 (1 ) 42,974 U.S. government and agency securities 3,014 5 — 3,019 Long-term: Corporate debt securities (one to two-year maturity) 38,207 277 (17 ) 38,467 U.S. government and agency securities (one to two-year maturity) 898 6 — 904 $ 219,482 $ 665 $ (33 ) $ 220,114 The following table summarizes our investments in corporate debt securities, commercial paper, and U.S. government and agency securities, classified as available-for-sale as of December 31, 2019 (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Loss Fair Value Short-term: Corporate debt securities $ 89,110 $ 12 $ (43 ) $ 89,079 Commercial paper 39,004 18 — 39,022 U.S. government and agency securities 4,990 7 — 4,997 Long-term: Corporate debt securities (one to two-year maturity) 2,017 — (1 ) 2,016 $ 135,121 $ 37 $ (44 ) $ 135,114 We review investments whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. We evaluate whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, we consider the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected from the security is compared to the amortized cost basis of the security. If the present value of cash flows expected to be collected is less than the amortized cost basis, a credit loss exists and an allowance for credit losses is recorded for the credit loss on our condensed consolidated balance sheet, limited by the amount that the fair value is less than the amortized cost basis. Any impairment that is not related to a credit loss is recognized in other comprehensive income (loss). Changes in the allowance for credit losses are recorded as a provision for (or reversal of) credit loss expense. Losses are charged against the allowance when we believe the uncollectability of an available-for-sale security is confirmed or when either of the criteria regarding intent or requirement to sell is met. The unrealized losses at September 30, 2020 and December 31, 2019 were attributable to changes in interest rates and we do not believe any unrealized losses represent credit losses. We held 27 commercial paper and corporate debt securities at both September 30, 2020 and December 31, 2019, that were in an unrealized loss position. The following table summarizes these available-for-sale securities in an unrealized loss position for which an allowance for credit losses has not been recorded at September 30, 2020, aggregated by major security type and length of time in a continuous unrealized loss position (in thousands): Less than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Commercial paper $ 11,987 $ (1 ) $ — $ — $ 11,987 $ (1 ) Corporate debt securities 50,709 (32 ) — — 50,709 (32 ) Total $ 62,696 $ (33 ) $ — $ — $ 62,696 $ (33 )

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	8. Net Loss Per Share Basic and diluted net loss per common share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Our potentially dilutive shares, which include outstanding stock options and unvested restricted stock units, are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. The following potentially dilutive securities were excluded from the calculation of diluted net loss per share due to their anti-dilutive effect (in thousands): As of September 30, 2020 2019 Outstanding stock options 11,180 10,211 Unvested restricted stock units 1,631 835 We have the option to settle the conversion obligation for our 3.00% convertible senior notes issued October 2018, and due 2025, in cash, shares or any combination of the two. As such notes were not convertible as of September 30, 2020, they are not participating securities and do not have an impact on the calculation of basic loss per share. Based on our net loss position, there was no impact to the calculation of dilutive loss per share during the three and nine months ended September 30, 2020 and 2019.

Stock-based Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	9. Stock-based Compensation The following table summarizes stock-based compensation expenses included in operating expenses for the periods indicated (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Cost of sales $ 29 $ 27 $ 91 $ 27 Research and development 2,687 1,593 7,668 4,785 Selling, general and administrative 3,797 2,099 10,334 6,930 Total stock-based compensation $ 6,513 $ 3,719 $ 18,093 $ 11,742

Equity

Equity	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Equity	10. Equity Underwritten Offerings On March 6, 2020, we completed a follow-on offering under our shelf registration statement on Form S-3 pursuant to which we issued an aggregate of 7,187,500 shares of common stock, which included the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $24.00 per share. We received aggregate net proceeds of approximately $161.8 million from the offering after deducting the underwriting discounts and commissions and other offering expenses. Open Market Sale Agreement On August 17, 2018, we entered into an Open Market Sale Agreement (the “Open Market Sale Agreement”) with Jefferies LLC, as agent (“Jefferies”), pursuant to which we may issue and sell shares of our common stock having an aggregate offering price of up to $75.0 million from time to time through Jefferies (the “Open Market Offering”). On May 5, 2020, we entered into Amendment No. 1 to the Open Market Sale Agreement, pursuant to which we increased the maximum aggregate offering price of shares of our common stock that we may issue and sell from time to time through Jefferies, by $100.0 million, from $75.0 million to up to $175.0 million (the “Open Market Shares”). Under the Open Market Sale Agreement, Jefferies may sell the Open Market Shares by methods deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended (the “Securities Act”). We may sell the Open Market Shares in amounts and at times to be determined by us from time to time subject to the terms and conditions of the Open Market Sale Agreement, but we have no obligation to sell any of the Open Market Shares in an Open Market Offering. We or Jefferies may suspend or terminate the offering of Open Market Shares upon notice to the other party and subject to other conditions. We have agreed to pay Jefferies commissions for its services in acting as agent in the sale of the Open Market Shares in the amount of up to 3.0% of gross proceeds from the sale of the Open Market Shares pursuant to the Open Market Sale Agreement. We have also agreed to provide Jefferies with customary indemnification and contribution rights. We did not sell Open Market Shares under the Open Market Sale Agreement during the three and nine months ended September 30, 2020. We sold an aggregate of 1.6 million Open Market Shares under the Open Market Sale Agreement, for net proceeds of approximately $14.6 million, during the three and nine months ended September 30, 2019.

Long-Term Obligations

Long-Term Obligations	9 Months Ended
	Sep. 30, 2020
3% Convertible Senior Notes Due 2025 [Member]
Long-Term Obligations	11. Long-Term Obligations 3.00% Convertible Senior Notes due 2025 In October 2018, we issued $172.5 million aggregate principal amount of convertible senior notes due 2025 (the “Notes”). The Notes were sold in a private offering to qualified institutional buyers in reliance on Rule 144A under the Securities Act. In accordance with accounting guidance for debt with conversion and other options, we separately account for the liability component (“Liability Component”) and the embedded conversion option (“Equity Component”) of the Notes by allocating the proceeds between the Liability Component and the Equity Component, due to our ability to settle the Notes in cash, shares of our common stock or a combination of cash and shares of our common stock, at our option. In connection with the issuance of the Notes, we incurred approximately $5.6 million of debt issuance costs, which primarily consisted of underwriting, legal and other professional fees, and allocated these costs between the Liability Component and the Equity Component based on the allocation of the proceeds. Of the total debt issuance costs, $2.2 million was allocated to the Equity Component and recorded as a reduction to additional paid-in capital, and $3.4 million was allocated to the Liability Component and recorded as a reduction of the Notes. The portion allocated to the Liability Component is amortized to interest expense using the effective interest method over seven years. The Notes are senior unsecured obligations and bear interest at a rate of 3.00% per year, payable semi-annually in arrears on April 15 and October 15 of each year, beginning on April 15, 2019. The Notes will be subject to redemption at our option, on or after October 15, 2022, in whole or in part, if the conditions described below are satisfied. The Notes will mature on October 15, 2025, unless earlier converted, redeemed or repurchased in accordance with their terms. Subject to satisfaction of certain conditions and during the periods described below, the Notes may be converted at an initial conversion rate of 63.0731 shares of common stock per $1 principal amount of the Notes (equivalent to an initial conversion price of approximately $15.85 per share of common stock). Holders of the Notes may convert all or any portion of their Notes, in multiples of $1 principal amount, at their option at any time prior to the close of business on the business day immediately preceding June 15, 2025 only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on December 31, 2018 (and only during such calendar quarter), if the last reported sale price of our common stock for at least 20 trading days (whether or not consecutive) during the period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price for the Notes on each applicable trading day; (2) during the five business day period immediately after any five consecutive trading day period (the “Measurement Period”) in which the trading price per $1,000 principal amount of Notes for each trading day of the Measurement Period was less than 98% of the product of the last reported sale price of our common stock and the conversion rate on each such trading day; (3) if we call the Notes for redemption, until the close of business on the business day immediately preceding the redemption date; or (4) upon the occurrence of specified corporate events as described within the indenture governing the Notes. As of September 30, 2020, none of the above circumstances had occurred and as such, the Notes could not have been converted. We may not redeem the Notes prior to October 15, 2022. On or after October 15, 2022, we may redeem for cash all or part of the Notes at our option if the last reported sale price of our common stock equals or exceeds 130% of the conversion price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period ending within five trading days prior to the date on which we send any notice of redemption. The redemption price will be 100% of the principal amount of the Notes to be redeemed, plus accrued and unpaid interest, if any. In addition, calling any convertible note for redemption will constitute a make-whole fundamental change with respect to that convertible note, in which case the conversion rate applicable to the conversion of that convertible note, if it is converted in connection with the redemption, will be increased in certain circumstances. The initial carrying amount of the Liability Component of $101.2 million was calculated by measuring the fair value of a similar liability that does not have an associated convertible feature. The allocation was performed in a manner that reflected our non-convertible borrowing rate for similar debt. The $67.9 million Equity Component of the Notes was recognized as a debt discount and represents the difference between $172.5 million proceeds from the issuance of the Notes and approximately $104.7 million fair value of the liability of the Notes on their respective dates of issuance. The excess of the principal amount of the Liability Component over its carrying amount is amortized to interest expense using the effective interest method over seven years. The Equity Component is not remeasured as long as it continues to meet the conditions for equity classification. The outstanding balances of the Notes as of September 30, 2020 consisted of the following (in thousands): Outstanding Balances Liability component: Principal $ 172,500 Less: debt discount and issuance costs, net (56,698 ) Net carrying amount $ 115,802 Equity component: $ 65,641 We determined the expected life of the Notes was equal to its seven-year term. The effective interest rate on the Liability Component of the Notes was 11.85%. As of September 30, 2020, the “if-converted value” did not exceed the remaining principal amount of the Notes. The fair value of the Notes was determined based on data points other than quoted prices that are observable, either directly or indirectly, and has been classified as Level 2 within the fair value hierarchy. The fair value of the Notes, which differs from their carrying value, is influenced by market interest rates, our stock price and stock price volatility. The estimated fair value of the Notes as of September 30, 2020 was approximately $206.4 million. The following table sets forth total interest expense recognized related to the Notes for the periods indicated (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Contractual interest expense $ 1,293 $ 1,300 $ 3,881 $ 3,882 Amortization of debt discount 1,929 1,703 5,661 5,045 Amortization of debt issuance costs 97 86 284 253 Total interest expense $ 3,319 $ 3,089 $ 9,826 $ 9,180 Future minimum payments on the Notes as of September 30, 2020 were as follows (in thousands): Years ended December 31, Future Minimum Payments 2020 $ 2,588 2021 5,175 2022 5,175 2023 5,175 2024 and thereafter 182,850 Total minimum payments $ 200,963 Less: interest (28,463 ) Less: unamortized discount (56,698 ) Convertible senior notes $ 115,802 Deferred Royalty Obligation In September 2019, we entered into a Revenue Interest Financing Agreement (“deferred royalty obligation”) with HealthCare Royalty Partners III, L.P. and HealthCare Royalty Partners IV, L.P. (“HCR”) whereby HCR receives payments from us at a tiered percentage (the “Applicable Tiered Percentage”) of net revenues of XPOVIO and any of our other future products, including worldwide net product sales and upfront payments, milestones, and royalties. We received $75.0 million upon closing (the “First Investment Amount”) and have the right to receive an additional $75.0 million (the “Second Investment Amount” and together with the First Investment Amount, the “Investment Amount”) upon the achievement of future regulatory and commercial milestones and subject to the approval of both parties. In exchange for the First Investment Amount, HCR receives tiered royalties in the mid-single digits based on worldwide net revenues of XPOVIO and any of our other future products, including worldwide net product sales and upfront payments, milestones, and royalties. The Applicable Tiered Percentages are subject to reduction in the future if a target based on cumulative U.S. net sales is met. Total royalty payments are capped at 185% of the Investment Amount. If HCR has not received 65% of the Investment Amount by December 31, 2022 or 100% of the Investment Amount by December 31, 2024, we must make a cash payment sufficient to gross up the payments to such minimum amounts. As the repayment of the funded amount is contingent upon worldwide net product sales and upfront payments, milestones, and royalties, the repayment term may be shortened or extended depending on actual worldwide net product sales and upfront payments, milestones, and royalties. The repayment period commenced on October 1, 2019 and expires on the earlier of (i) the date in which HCR has received cash payments totaling an aggregate of 185% of the Investment Amount or (ii) the legal maturity date of October 1, 2031. If HCR has not received payments equal to 185% of the Investment Amount by the twelve-year anniversary of the initial closing date, we shall pay an amount equal to the Investment Amount plus a specific annual rate of return less payments previously received. As of September 30, 2020, we have made $4.6 million in payments to HCR. We have evaluated the terms of the deferred royalty obligation and concluded that the features of the Investment Amount are similar to those of a debt instrument. Accordingly, we have accounted for the transaction as long-term debt. We have evaluated the terms of the debt and determined that the repayment of 185% of the Investment Amount, less any payments made to date, upon a change of control is an embedded derivative that requires bifurcation from the debt instrument and fair value recognition. We determine the fair value of the derivative using an option pricing Monte Carlo simulation model taking into account the probability of change of control occurring and potential repayment amounts and timing of such payments that would result under various scenarios, as further described in Note 2, “ Summary of Significant Accounting Policies Long-Term Obligations The effective interest rate as of September 30, 2020 was approximately 18.1%. In connection with the deferred royalty obligation, we incurred debt issuance costs totaling $1.4 million in the quarter ended September 30, 2019. Debt issuance costs have been netted against the debt and are being amortized over the estimated term of the debt using the effective interest method, adjusted on a prospective basis for changes in the underlying assumptions and inputs. The assumptions used in determining the expected repayment term of the debt and amortization period of the issuance costs require that we make estimates that could impact the short and long-term classification of these costs, as well as the period over which these costs will be amortized. The carrying value of the deferred royalty obligation, as presented on our condensed consolidated balance sheet, approximates fair value at September 30, 2020 and was measured using Level 3 inputs. The estimated fair market value was calculated using an option pricing Monte Carlo simulation model with inputs consistent with those used in determining the embedded derivative values as described in Note 2, “ Summary of Significant Accounting Policies Long-Term Obligations

Nature of Business and Basis _2

Nature of Business and Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, all adjustments (including those which are normal and recurring) considered necessary for a fair presentation of the interim financial information have been included. When preparing financial statements in conformity with GAAP, we must make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, expenses and related disclosures at the date of the financial statements. Actual results could differ from those estimates. Additionally, operating results for the three and nine months ended September 30, 2020 are not necessarily indicative of the results that may be expected for any other interim period or for the fiscal year ending December 31, 2020. For further information, refer to the financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2019 as filed with the Securities and Exchange Commission (“SEC”) on February 26, 2020 (“Annual Report”).
Basis of Consolidation	Basis of Consolidation The condensed consolidated financial statements at September 30, 2020 include the accounts of Karyopharm Therapeutics Inc. and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The significant accounting policies used in preparation of these condensed consolidated financial statements on Form 10-Q are consistent with those discussed in Note 2, “ Summary of Significant Accounting Policies
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement - Disclosure Framework-Changes to the Disclosure Requirement for Fair Value Measurement (“ASU 2018-13”). The amendments in ASU 2018-13 modify the disclosure requirements on fair value measurements in Accounting Standards Codification (“ASC”) 820, Fair Value Measurement , based on the concepts in the FASB Concepts Statement, including the consideration of costs and benefits. The amendments under ASU 2018-13 are effective for interim and annual fiscal periods beginning after December 15, 2019, with early adoption permitted. We adopted this guidance effective January 1, 2020. The adoption of this standard did not have a material impact on our condensed consolidated financial statements. Recently Issued Accounting Standard In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging— Contracts in Entity’s Own Equity (Subtopic 815-40) the changes are a trade-off between simplifications in the accounting model, including no separation of an “equity” component to impute a market interest rate, as well as simpler analysis of embedded equity features, and a potentially adverse impact to diluted earnings per share (“EPS”) by requiring the use of the if-converted method.

Product Revenue (Tables)

Product Revenue (Tables)	9 Months Ended
	Sep. 30, 2020
XPOVIO [Member]
Summary of Product Revenue	To date, our only source of product revenue has been from the U.S. sales of XPOVIO, which we began shipping to our customers in July 2019. Net product revenue, including provisions primarily consisting of distribution fees and cash discounts, as well as reserves for chargebacks, rebates and returns, were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Gross product revenue $ 25,322 $ 14,960 $ 66,440 $ 14,960 Provision for product revenue (3,992 ) (2,139 ) (10,448 ) (2,139 ) Total product revenue, net $ 21,330 $ 12,821 $ 55,992 $ 12,821

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Schedule of Inventory, Current	The following table presents our inventory of XPOVIO (in thousands): September 30, 2020 December 31, 2019 Raw materials and work in process $ 1,566 $ 273 Finished goods 445 73 Total inventory $ 2,011 $ 346

License and Asset Purchase Ag_2

License and Asset Purchase Agreements (Tables)	9 Months Ended
	Sep. 30, 2020
Revenue From Contract With Customer [Abstract]
Changes In Balance Sheet Accounts For Outlicensing And Asset Sale Agreements	As summarized in the following table, which presents changes in balance sheet accounts for our out-licensing and asset purchase agreements, we recognized $2.3 million under the Original Antengene Agreement and $2.2 million upon termination of the license agreement with Ono during the nine months ended September 30, 2020 (in thousands): December 31, 2019 Additions Deductions September 30, 2020 Short-term Deferred Revenue Original Antengene Agreement $ 2,341 $ — $ (2,341 ) $ — Amended Antengene Agreement — 297 — 297 Total short-term deferred revenue $ 2,341 $ 297 $ (2,341 ) $ 297 Long-term Deferred Revenue Ono $ 2,192 $ — $ (2,192 ) $ — Total long-term deferred revenue $ 2,192 $ — $ (2,192 ) $ — Total deferred revenue $ 4,533 $ 297 $ (4,533 ) $ 297

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Schedule of Financial Assets That Have Been Measured at Fair Value	The following table presents information about our financial assets and liability that have been measured at fair value at September 30, 2020 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands): Description Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets Cash equivalents: Money market funds $ 29,555 $ 29,555 $ — $ — U.S. government and agency securities 8,998 8,998 — — Investments: Short-term: Corporate debt securities 134,750 — 134,750 — Commercial paper 42,974 — 42,974 — U.S. government and agency securities 3,019 — 3,019 — Long-term: Corporate debt securities (one to two-year maturity) 38,467 — 38,467 — U.S. government and agency securities (one to two-year maturity) 904 — 904 — $ 258,667 $ 38,553 $ 220,114 $ — Financial liability Embedded derivative liability $ 2,300 $ — $ — $ 2,300 The following table presents information about our financial assets and liability that have been measured at fair value at December 31, 2019 and indicates the fair value hierarchy of the valuation inputs utilized to determine such fair value (in thousands): Description Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets Cash equivalents: Money market funds $ 71,380 $ 71,380 $ — $ — Investments: Short-term: Corporate debt securities 89,079 — 89,079 — Commercial paper 39,022 — 39,022 — U.S. government and agency securities 4,997 — 4,997 — Long-term: Corporate debt securities (one to two-year maturity) 2,016 — 2,016 — $ 206,494 $ 71,380 $ 135,114 $ — Financial liability Embedded derivative liability $ 2,300 $ — $ — $ 2,300

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2020
Investments Debt And Equity Securities [Abstract]
Summary of Investments, Classified as Available-for-Sale	The following table summarizes our investments in corporate debt securities, commercial paper, and U.S. government and agency securities, classified as available-for-sale, as of September 30, 2020 (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Loss Fair Value Short-term: Corporate debt securities $ 134,394 $ 371 $ (15 ) $ 134,750 Commercial paper 42,969 6 (1 ) 42,974 U.S. government and agency securities 3,014 5 — 3,019 Long-term: Corporate debt securities (one to two-year maturity) 38,207 277 (17 ) 38,467 U.S. government and agency securities (one to two-year maturity) 898 6 — 904 $ 219,482 $ 665 $ (33 ) $ 220,114 The following table summarizes our investments in corporate debt securities, commercial paper, and U.S. government and agency securities, classified as available-for-sale as of December 31, 2019 (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Loss Fair Value Short-term: Corporate debt securities $ 89,110 $ 12 $ (43 ) $ 89,079 Commercial paper 39,004 18 — 39,022 U.S. government and agency securities 4,990 7 — 4,997 Long-term: Corporate debt securities (one to two-year maturity) 2,017 — (1 ) 2,016 $ 135,121 $ 37 $ (44 ) $ 135,114
Debt Securities Available-For-Sale	We held 27 commercial paper and corporate debt securities at both September 30, 2020 and December 31, 2019, that were in an unrealized loss position. The following table summarizes these available-for-sale securities in an unrealized loss position for which an allowance for credit losses has not been recorded at September 30, 2020, aggregated by major security type and length of time in a continuous unrealized loss position (in thousands): Less than 12 Months 12 Months or Longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Commercial paper $ 11,987 $ (1 ) $ — $ — $ 11,987 $ (1 ) Corporate debt securities 50,709 (32 ) — — 50,709 (32 ) Total $ 62,696 $ (33 ) $ — $ — $ 62,696 $ (33 )

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of Potentially Dilutive Securities Were Excluded From The Calculation of Diluted Net Loss Per Share Due to Their Anti-Dilutive Effect	The following potentially dilutive securities were excluded from the calculation of diluted net loss per share due to their anti-dilutive effect (in thousands): As of September 30, 2020 2019 Outstanding stock options 11,180 10,211 Unvested restricted stock units 1,631 835

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Total Stock-based Compensation Expense Recognized in Connection with All Share-based Payment Awards	The following table summarizes stock-based compensation expenses included in operating expenses for the periods indicated (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Cost of sales $ 29 $ 27 $ 91 $ 27 Research and development 2,687 1,593 7,668 4,785 Selling, general and administrative 3,797 2,099 10,334 6,930 Total stock-based compensation $ 6,513 $ 3,719 $ 18,093 $ 11,742

Long-Term Obligations (Tables)

Long-Term Obligations (Tables) - 3% Convertible Senior Notes Due 2025 [Member]	9 Months Ended
	Sep. 30, 2020
Summary of Outstanding Balances of Convertible Notes	The outstanding balances of the Notes as of September 30, 2020 consisted of the following (in thousands): Outstanding Balances Liability component: Principal $ 172,500 Less: debt discount and issuance costs, net (56,698 ) Net carrying amount $ 115,802 Equity component: $ 65,641
Schedule of Interest Expense Recognized Related to Convertible Notes	The following table sets forth total interest expense recognized related to the Notes for the periods indicated (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Contractual interest expense $ 1,293 $ 1,300 $ 3,881 $ 3,882 Amortization of debt discount 1,929 1,703 5,661 5,045 Amortization of debt issuance costs 97 86 284 253 Total interest expense $ 3,319 $ 3,089 $ 9,826 $ 9,180
Summary of Future Minimum Payments on Convertible Notes	Future minimum payments on the Notes as of September 30, 2020 were as follows (in thousands): Years ended December 31, Future Minimum Payments 2020 $ 2,588 2021 5,175 2022 5,175 2023 5,175 2024 and thereafter 182,850 Total minimum payments $ 200,963 Less: interest (28,463 ) Less: unamortized discount (56,698 ) Convertible senior notes $ 115,802

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements - Additional Information (Detail) $ in Trillions	1 Months Ended
	Mar. 31, 2020USD ($)
Covid19 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unusual Loss	$ 2.2

Product Revenue - Summary of Pr

Product Revenue - Summary of Product Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Total product revenue, net	$ 21,333	$ 13,149	$ 72,985	$ 22,797
Product revenue
Gross product revenue	25,322	14,960	66,440	14,960
Provision for product revenue	(3,992)	(2,139)	(10,448)	(2,139)
Total product revenue, net	$ 21,330	$ 12,821	$ 55,992	$ 12,821

Product Revenue - Additional In

Product Revenue - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Revenue From Contract With Customer [Abstract]
Accounts receivable	$ 11,062,000	$ 7,862,000
Bad debt write-offs	0
Credit losses	$ 0	$ 0

Inventory - Schedule of Invento

Inventory - Schedule of Inventory Current (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw materials and work in process	$ 1,566	$ 273
Finished goods	445	73
Total inventory	$ 2,011	$ 346

License and Asset Purchase Ag_3

License and Asset Purchase Agreements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	May 31, 2020
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenues	$ 21,333	$ 13,149	$ 72,985	$ 22,797
Unrecognized deferred revenue					$ 1,300
License and other revenue	21,333	$ 13,149	72,985	$ 22,797
Ono Pharmaceutical Company Limited [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payments receivable			2,200
Amended Antengene Agreement [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Performance obligations					13,000
Amended Antengene Agreement [Member] | Selinexor and KPT-9274 [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Cumulative adjustment to license revenue			12,700
Amended Antengene Agreement [Member] | Eltanexor [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront payments	300		300
Up-front Payment Arrangement [Member] | Amended Antengene Agreement [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Performance obligations					11,700
Ono Pharmaceutical Company Limited and Antengene Therapeutics Limited [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenues			$ 2,200
Type of revenue [extensible list]			kpti:LicenseAndOtherMember
License and other revenue			$ 2,200
Ono Pharmaceutical Company Limited and Antengene Therapeutics Limited [Member] | Government Research Grant Agreement [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Total revenues			14,900
License and other revenue			14,900
Antengene Therapeutics Limited [Member] | Government Research Grant Agreement [Member] | Sales Milestone Events [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Milestone payments receivable			2,300
Antengene Therapeutics Limited [Member] | Up-front Payment Arrangement [Member] | Government Research Grant Agreement [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront payments	$ 11,700		$ 11,700		11,700
Performance obligations					$ 11,700

License and Asset Purchase Ag_4

License and Asset Purchase Agreements - Changes In Balance Sheet Accounts For Outlicensing And Asset Sale Agreements (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Beginning Period	$ 2,341
Deferred revenue current period increase	297
Deferred revenue current period decrease	(2,341)
Ending Period	297
Beginning Period	2,192
Deferred revenue noncurrent period decrease	(2,192)
Beginning Period	4,533
Deferred revenue increase	297
Deferred revenue decrease	(4,533)
Ending Period	297
Antengene Therapeutics Limited [Member]
Beginning Period	2,341
Deferred revenue current period decrease	(2,341)
Ono Pharmaceutical Company Limited [Member]
Beginning Period	2,192
Deferred revenue noncurrent period decrease	(2,192)
Amended Antengene Agreement [Member]
Deferred revenue current period increase	297
Ending Period	$ 297

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Schedule of Financial Assets That Have Been Measured at Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial assets
Total	$ 258,667	$ 206,494
Financial liability
Embedded derivative liability	2,300	2,300
Money Market Funds [Member]
Financial assets
Cash equivalents	29,555	71,380
Long-term [Member] | Certificates of Deposit [Member]
Financial assets
Investments	38,467	2,016
Level 1 [Member]
Financial assets
Total	38,553	71,380
Level 1 [Member] | Money Market Funds [Member]
Financial assets
Cash equivalents	29,555	71,380
Level 2 [Member]
Financial assets
Total	220,114	135,114
Level 2 [Member] | Long-term [Member] | Certificates of Deposit [Member]
Financial assets
Investments	38,467	2,016
Level 3 [Member]
Financial liability
Embedded derivative liability	2,300	2,300
US Government Agencies Debt Securities | Money Market Funds [Member]
Financial assets
Cash equivalents	8,998
US Government Agencies Debt Securities | Short-term [Member]
Financial assets
Investments	3,019	4,997
US Government Agencies Debt Securities | Long-term [Member]
Financial assets
Investments	904
US Government Agencies Debt Securities | Level 1 [Member] | Money Market Funds [Member]
Financial assets
Cash equivalents	8,998
US Government Agencies Debt Securities | Level 2 [Member] | Short-term [Member]
Financial assets
Investments	3,019	4,997
US Government Agencies Debt Securities | Level 2 [Member] | Long-term [Member]
Financial assets
Investments	904
Corporate Debt Securities [Member] | Short-term [Member]
Financial assets
Investments	134,750	89,079
Corporate Debt Securities [Member] | Level 2 [Member] | Short-term [Member]
Financial assets
Investments	134,750	89,079
Commercial Paper [Member] | Short-term [Member]
Financial assets
Investments	42,974	39,022
Commercial Paper [Member] | Level 2 [Member] | Short-term [Member]
Financial assets
Investments	$ 42,974	$ 39,022

Investments - Summary of Invest

Investments - Summary of Investments, Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 219,482	$ 135,121
Gross Unrealized Gains	665	37
Gross Unrealized Loss	(33)	(44)
Fair Value	220,114	135,114
Short-term [Member] | Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	134,394	89,110
Gross Unrealized Gains	371	12
Gross Unrealized Loss	(15)	(43)
Fair Value	134,750	89,079
Short-term [Member] | Commercial Paper [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	42,969	39,004
Gross Unrealized Gains	6	18
Gross Unrealized Loss	(1)
Fair Value	42,974	39,022
Short-term [Member] | US Government Agencies Debt Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,014	4,990
Gross Unrealized Gains	5	7
Fair Value	3,019	4,997
Long-term [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	38,207
Gross Unrealized Gains	277
Gross Unrealized Loss	(17)
Fair Value	38,467
Long-term [Member] | Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		2,017
Gross Unrealized Loss		(1)
Fair Value		$ 2,016
Long-term [Member] | US Government Agencies Debt Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	898
Gross Unrealized Gains	6
Fair Value	$ 904

Investments - Additional Inform

Investments - Additional Information (Detail)	Sep. 30, 2020USD ($)Security	Dec. 31, 2019USD ($)Security
Investments Debt And Equity Securities [Abstract]
Unrealized losses, other-than-temporary impairments | $	$ 0	$ 0
Number of debt securities with unrealized loss position for less than one year | Security	27	27

Investments - Debt Securities A

Investments - Debt Securities Available-For-Sale (Detail) $ in Thousands	Sep. 30, 2020USD ($)
Fair Value, Less than 12 Months	$ 62,696
Unrealized Losses, Less than 12 Months	(33)
Fair Value	62,696
Unrealized Losses	(33)
Commercial Paper [Member]
Fair Value, Less than 12 Months	11,987
Unrealized Losses, Less than 12 Months	(1)
Fair Value	11,987
Unrealized Losses	(1)
Corporate Debt Securities [Member]
Fair Value, Less than 12 Months	50,709
Unrealized Losses, Less than 12 Months	(32)
Fair Value	50,709
Unrealized Losses	$ (32)

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Potentially Dilutive Securities Were Excluded From The Calculation of Diluted Net Loss Per Share Due to Their Anti-Dilutive Effect (Detail) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Outstanding Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from the calculation of diluted net loss per share due to anti-dilutive effect (in shares)	11,180	10,211
Unvested Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Dilutive securities excluded from the calculation of diluted net loss per share due to anti-dilutive effect (in shares)	1,631	835

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Detail) - 3% Convertible Senior Notes Due 2025 [Member]	Oct. 18, 2018	Oct. 16, 2018	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Notes, maturity date		Oct. 15, 2025	Oct. 15, 2025
Notes, interest rate	3.00%		11.85%

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Total Stock-based Compensation Expense Recognized in Connection with All Share-based Payment Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,513	$ 3,719	$ 18,093	$ 11,742
Cost of Sales [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	29	27	91	27
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	2,687	1,593	7,668	4,785
Selling,General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 3,797	$ 2,099	$ 10,334	$ 6,930

Equity - Controlled Equity Offe

Equity - Controlled Equity Offering Sales Agreement - Additional Information (Detail) - USD ($)	Mar. 06, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	May 05, 2020	May 04, 2020	Aug. 17, 2018
Open Market Sale Agreement [Member]
Equity Offering [Line Items]
Number of shares of common stock sold in public offering		0	1,600,000	0	1,600,000
Net proceeds from sale of common stock			$ 14,600,000		$ 14,600,000
Maximum [Member] | Jefferies LLC [Member] | Open Market Sale Agreement Amendment [Member]
Equity Offering [Line Items]
Aggregate offering price						$ 175,000,000	$ 75,000,000	$ 75,000,000
Additional aggregate offering price						$ 100,000,000
Maximum [Member] | Jefferies LLC [Member] | Open Market Sale Agreement [Member]
Equity Offering [Line Items]
Percentage of commission of gross proceeds from the sale of Shares				3.00%
Common Stock [Member]
Equity Offering [Line Items]
Number of shares of common stock sold in public offering	7,187,500		1,634,000	7,188,000	1,634,000
Public offering price of common shares	$ 24
Net proceeds after deducting underwriting discounts, commissions and offering expenses	$ 161,800,000

Long-Term Obligations - Additio

Long-Term Obligations - Additional Information (Detail)	Oct. 15, 2022d	Oct. 18, 2018	Oct. 16, 2018USD ($)$ / sharesshares	Jun. 30, 2020d	Sep. 30, 2020USD ($)d	Sep. 30, 2019USD ($)
Subsequent Event [Line Items]
Notes, conversion price per share | $ / shares			$ 1
Debt instrument convertible threshold consecutive trading days | d				5
Description of debt instrument convertible period					during the five business day period immediately after any five consecutive trading day
Principal amount of notes used in conversion rate					$ 1,000
Debt instrument convertible threshold maximum percentage of product of last reported sale price of common stock					98.00%
Equity component of convertible notes recognized as debt discount					$ 67,900,000
Proceeds from issuance of convertible notes					172,500,000
Fair value of liability of convertible notes					$ 104,700,000
Expected life of convertible notes					7 years
Debt instrument, convertible, if-converted value in excess of principal					$ 0
Estimated fair value of convertible notes					206,400,000
HealthCare Royalty Partners IV LP [Member]
Subsequent Event [Line Items]
Repayment of deffered royalty obligation to HCR					4,600,000
Revenue Interest Financing Agreement [Member]
Subsequent Event [Line Items]
Debt issuance costs						$ 1,400,000
First investment amount						75,000,000
Second investment amount						$ 75,000,000
Aggregate Royalties Percentage						185.00%
Embedded Derivative, Fair Value					$ 2,300,000
Debt Instrument Interest Rate					18.10%
Revenue Interest Financing Agreement [Member] | HealthCare Royalty Partners IV LP [Member]
Subsequent Event [Line Items]
Aggregate Royalties Percentage					185.00%
Revenue Interest Financing Agreement [Member] | HealthCare Royalty Partners IV LP [Member] | Royalty Due On December 31, 2022 [Member]
Subsequent Event [Line Items]
Royalty Payable Percentage					65.00%
Revenue Interest Financing Agreement [Member] | HealthCare Royalty Partners IV LP [Member] | Royalty Due On December 31, 2024 [Member]
Subsequent Event [Line Items]
Royalty Payable Percentage					100.00%
Convertible Note Offering [Member]
Subsequent Event [Line Items]
Notes converted in to common stock, amount | shares			63.0731
Notes, conversion price per share | $ / shares			$ 15.85
3% Convertible Senior Notes Due 2025 [Member]
Subsequent Event [Line Items]
Aggregate principal amount			$ 172,500,000
Debt issuance costs					$ 5,600,000
Debt issuance costs allocated to equity component and recorded as a reduction to additional paid-in capital					2,200,000
Debt issuance costs allocated to liability component and recorded as a reduction of convertible notes					$ 3,400,000
Debt discount and issuance costs amortized to interest expense, amortization period					7 years
Notes, interest rate		3.00%			11.85%
Notes, maturity date			Oct. 15, 2025		Oct. 15, 2025
Principal amount of notes used in conversion rate					$ 1
Debt instrument, convertible latest date					Jun. 15, 2025
Notes instrument, trading days | d					20
Debt instrument convertible threshold consecutive trading days | d					30
Notes conversion price, percentage					130.00%
Initial amount of liability component					$ 101,200,000
Equity component of convertible notes recognized as debt discount					$ 65,641,000
3% Convertible Senior Notes Due 2025 [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Notes instrument, trading days | d	20
Debt instrument convertible threshold consecutive trading days | d	30
Notes conversion price, percentage	130.00%
Notes, repurchase price	100.00%

Long-Term Obligations - Summary

Long-Term Obligations - Summary of Outstanding Balances of Convertible Notes (Detail) $ in Thousands	Sep. 30, 2020USD ($)
Liability component:
Equity component	$ 67,900
3% Convertible Senior Notes Due 2025 [Member]
Liability component:
Principal	172,500
Less: debt discount and issuance costs, net	(56,698)
Net carrying amount	115,802
Equity component	$ 65,641

Long-Term Obligations - Schedul

Long-Term Obligations - Schedule of Interest Expense Recognized Related to Convertible Notes (Detail) - 3% Convertible Senior Notes Due 2025 [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Contractual interest expense	$ 1,293	$ 1,300	$ 3,881	$ 3,882
Amortization of debt discount	1,929	1,703	5,661	5,045
Amortization of debt issuance costs	97	86	284	253
Total interest expense	$ 3,319	$ 3,089	$ 9,826	$ 9,180

Long-Term Obligations - Summa_2

Long-Term Obligations - Summary of Future Minimum Payments on Convertible Notes (Detail) - 3% Convertible Senior Notes Due 2025 [Member] $ in Thousands	Sep. 30, 2020USD ($)
Debt Instrument [Line Items]
2020	$ 2,588
2021	5,175
2022	5,175
2023	5,175
2024 and thereafter	182,850
Total minimum payments	200,963
Less: interest	(28,463)
Less: unamortized discount	(56,698)
Convertible senior notes	$ 115,802