Exelixis (EXEL) 10-Q 30 Oct 19 2019 Q3 Quarterly report Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 27, 2019	Oct. 21, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Amendment Flag	false
Document Period End Date	Sep. 27, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Document Transition Report	false
Entity File Number	000-30235
Entity Registrant Name	EXELIXIS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3257395
Entity Central Index Key	0000939767
Current Fiscal Year End Date	--01-03
Entity Address, Address Line One	1851 Harbor Bay Parkway
Entity Address, City or Town	Alameda,
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94502
City Area Code	650
Local Phone Number	837-7000
Title of 12(b) Security	Common Stock $.001 Par Value per Share
Trading Symbol	EXEL
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		303,846,306

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018	[1]
Current assets:
Cash and cash equivalents	$ 242,317	$ 314,775
Short-term investments	518,350	378,559
Trade receivables, net	169,788	162,771
Other receivables	13,801	16,056
Inventory, net	13,366	9,838
Prepaid expenses and other current assets	14,490	15,017
Total current assets	972,112	897,016
Long-term investments	486,763	157,187
Long-term restricted cash and investments	1,000	1,100
Property and equipment, net	49,467	50,897
Operating lease right-of-use assets	17,735	5,867
Deferred tax assets, net	186,836	244,111
Goodwill	63,684	63,684
Other long-term assets	7,268	2,424
Total assets	1,784,865	1,422,286
Current liabilities:
Accounts payable	8,352	10,901
Accrued compensation and benefits	31,713	32,142
Accrued clinical trial liabilities	30,330	18,231
Rebates and fees due to customers	16,782	14,954
Accrued collaboration liabilities	7,973	7,419
Other current liabilities	45,919	21,825
Total current liabilities	141,069	105,472
Long-term portion of lease liabilities	23,705	12,178
Long-term portion of deferred revenue	15,399	15,897
Other long-term liabilities	975	1,286
Total liabilities	181,148	134,833
Commitments
Stockholders’ equity:
Preferred stock, $0.001 par value, 10,000,000 shares authorized and no shares issued	0	0
Common stock, $0.001 par value; 400,000,000 shares authorized; issued and outstanding: 303,776,032 and 299,876,080 at September 30, 2019 and December 31, 2018, respectively	304	300
Additional paid-in capital	2,228,839	2,168,217
Accumulated other comprehensive income (loss)	2,668	(701)
Accumulated deficit	(628,094)	(880,363)
Total stockholders’ equity	1,603,717	1,287,453
Total liabilities and stockholders’ equity	$ 1,784,865	$ 1,422,286
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 27, 2019	Dec. 28, 2018	[1]
Preferred stock
Par value (in dollars per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	10,000,000	10,000,000
Shares issued (in shares)	0	0
Common stock
Par value (in dollars per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	400,000,000	400,000,000
Shares issued (in shares)	303,776,032	299,876,080
Shares outstanding (in shares)	303,776,032	299,876,080
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Total revenues	$ 271,703	$ 225,397	$ 727,465	$ 625,224
Operating expenses:
Cost of goods sold	7,537	7,360	22,577	18,996
Research and development	97,295	44,741	242,516	124,986
Selling, general and administrative	51,265	48,120	170,218	153,989
Total operating expenses	156,097	100,221	435,311	297,971
Income from operations	115,606	125,176	292,154	327,253
Other income (expense), net:
Interest income	7,191	3,507	20,253	8,099
Other, net	(140)	271	688	368
Total other income (expense), net:	7,051	3,778	20,941	8,467
Income before income taxes	122,657	128,954	313,095	335,720
Provision for income taxes	(25,205)	(2,324)	(60,826)	(5,739)
Net income	$ 97,452	$ 126,630	$ 252,269	$ 329,981
Net income per share, basic (in dollars per share)	$ 0.32	$ 0.42	$ 0.84	$ 1.11
Net income per share, diluted (in dollars per share)	$ 0.31	$ 0.41	$ 0.80	$ 1.05
Shares used in computing net income per share, basic (in shares)	303,268	298,416	301,999	297,700
Shares used in computing net income per share, diluted (in shares)	315,453	312,346	315,046	313,200
Net product revenues
Total revenues	$ 191,768	$ 162,946	$ 565,024	$ 443,054
Collaboration revenue
Total revenues	$ 79,935	$ 62,451	$ 162,441	$ 182,170

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Statement of Comprehensive Income [Abstract]
Net income		$ 97,452	$ 126,630	$ 252,269	$ 329,981
Other comprehensive income (loss):
Net unrealized gains or losses on available-for-sale securities, net of tax impact of $___, $0, $___ and $0, respectively	[1]	461	218	3,369	(166)
Total other comprehensive income (loss)		461	218	3,369	(166)
Comprehensive income		$ 97,913	$ 126,848	$ 255,638	$ 329,815
[1]	Reclassification adjustments to net income resulting from realized gains or losses on the sale of securities and the related tax impact were nominal or zero during the periods presented.

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Other comprehensive income (loss):
Unrealized gains or losses on available-for-sale securities, tax impact	$ (129)	$ 0	$ (936)	$ 0
Reclassification adjustments to net income resulting from realized gains or losses on sale of securities	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total		Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance (in shares) at Dec. 29, 2017			296,209,426
Balance at Dec. 29, 2017	$ 284,961		$ 296	$ 2,114,184	$ (347)	$ (1,829,172)
Net income	329,981					329,981
Other comprehensive income (loss)	(166)				(166)
Issuance of common stock under equity incentive and stock purchase plans (in shares)			2,672,458
Issuance of common stock under equity incentive and stock purchase plans	14,121		$ 3	14,118
Stock-based compensation	28,330			28,330
Balance (in shares) at Sep. 28, 2018			298,881,884
Balance at Sep. 28, 2018	915,966		$ 299	2,156,632	(513)	(1,240,452)
Balance (in shares) at Jun. 29, 2018			297,892,180
Balance at Jun. 29, 2018	775,202		$ 298	2,142,717	(731)	(1,367,082)
Net income	126,630					126,630
Other comprehensive income (loss)	218				218
Issuance of common stock under equity incentive and stock purchase plans (in shares)			989,704
Issuance of common stock under equity incentive and stock purchase plans	4,174		$ 1	4,173
Stock-based compensation	9,742			9,742
Balance (in shares) at Sep. 28, 2018			298,881,884
Balance at Sep. 28, 2018	$ 915,966		$ 299	2,156,632	(513)	(1,240,452)
Balance (in shares) at Dec. 28, 2018	299,876,080	[1]	299,876,080
Balance at Dec. 28, 2018	$ 1,287,453	[1]	$ 300	2,168,217	(701)	(880,363)
Net income	252,269					252,269
Other comprehensive income (loss)	3,369				3,369
Issuance of common stock under equity incentive and stock purchase plans (in shares)			3,899,952
Issuance of common stock under equity incentive and stock purchase plans	19,879		$ 4	19,875
Stock-based compensation	$ 40,747			40,747
Balance (in shares) at Sep. 27, 2019	303,776,032		303,776,032
Balance at Sep. 27, 2019	$ 1,603,717		$ 304	2,228,839	2,668	(628,094)
Balance (in shares) at Jun. 28, 2019			302,784,854
Balance at Jun. 28, 2019	1,488,632		$ 303	2,211,668	2,207	(725,546)
Net income	97,452					97,452
Other comprehensive income (loss)	461				461
Issuance of common stock under equity incentive and stock purchase plans (in shares)			991,178
Issuance of common stock under equity incentive and stock purchase plans	4,033		$ 1	4,032
Stock-based compensation	$ 13,139			13,139
Balance (in shares) at Sep. 27, 2019	303,776,032		303,776,032
Balance at Sep. 27, 2019	$ 1,603,717		$ 304	$ 2,228,839	$ 2,668	$ (628,094)
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands		9 Months Ended
		Sep. 27, 2019	Sep. 28, 2018
Statement of Cash Flows [Abstract]
Net income		$ 252,269	$ 329,981
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		6,088	2,876
Stock-based compensation		40,747	28,330
401(k) matching contributions made in common stock		4,079	3,232
Amortization and other changes in right-of-use assets		(6,367)	2,732
Deferred income taxes		56,339	0
Gain on other equity investments		(730)	(209)
Accretion of investments, net and other		(3,970)	(1,423)
Changes in operating assets and liabilities:
Trade receivables, net		(7,017)	(12,707)
Other receivables		2,469	(2,938)
Inventory, net		(3,528)	(3,776)
Current portion of unbilled collaboration revenue		(2,640)	(32,673)
Prepaid expenses and other current assets		527	(3,529)
Other long-term assets		(6,294)	(542)
Accounts payable		(2,708)	(1,248)
Accrued compensation and benefits		(429)	6,210
Accrued clinical trial liabilities		12,099	(891)
Rebates and fees due customers		1,828	4,124
Accrued collaboration liability		554	(577)
Current and long-term deferred revenue		3,592	(1,548)
Long-term portion of lease liabilities		6,087	(974)
Other current and long-term liabilities		15,940	(3,321)
Net cash provided by operating activities		368,935	311,129
Cash flows from investing activities:
Purchases of property and equipment		(5,575)	(30,403)
Proceeds from sale of property and equipment		0	308
Purchases of investments		(887,698)	(368,304)
Proceeds from maturities of investments		422,419	231,204
Proceeds from sale of investments		13,078	11,935
Proceeds from other equity investments		730	209
Net cash used in investing activities		(457,046)	(155,051)
Cash flows from financing activities:
Proceeds from exercise of stock options		14,811	10,390
Proceeds from employee stock purchase plan		4,145	3,650
Taxes paid related to net share settlement of equity awards		(3,369)	(3,205)
Principal payments on financing lease obligation		(34)	0
Net cash provided by financing activities		15,553	10,835
Net (decrease) increase in cash, cash equivalents and restricted cash		(72,558)	166,913
Cash, cash equivalents and restricted cash at beginning of period		315,875	188,314
Cash, cash equivalents and restricted cash at end of period		243,317	355,227
Supplemental cash flow disclosure:
Right-of-use assets obtained in exchange for lease obligations	[1]	12,944	17,180
Unpaid liabilities incurred to acquire Property and equipment		159	1,281
Unpaid liabilities incurred to acquire investments		$ 8,961	$ 0
[1]	Amounts for the nine months ended September 30, 2019 include receipt of a tenant incentive payment and an amendment to our existing lease for office and research space. Amounts for the nine months ended September 30, 2018 include the transition adjustment for the adoption of Topic 842.

Organization and Summary of Sig

Organization and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 27, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Organization Exelixis, Inc. (Exelixis, we, our or us) is an oncology-focused biotechnology company that strives to accelerate the discovery, development and commercialization of new medicines for difficult-to-treat cancers. Since we were founded in 1994, four products resulting from our discovery efforts have progressed through clinical development, received regulatory approval and have launched commercially. Two are derived from cabozantinib, an inhibitor of multiple tyrosine kinases including MET, AXL, VEGF receptors and RET. These are: CABOMETYX® (cabozantinib) tablets approved for advanced renal cell carcinoma (RCC) and previously treated hepatocellular carcinoma (HCC); and COMETRIQ® (cabozantinib) capsules approved for progressive, metastatic medullary thyroid cancer. The other two products resulting from our discovery efforts are: COTELLIC® (cobimetinib), an inhibitor of MEK, approved as part of a combination regimen to treat a specific form of advanced melanoma and marketed under a collaboration with Genentech, Inc. (a member of the Roche Group) (Genentech); and MINNEBRO® (esaxerenone), an oral, non-steroidal, selective blocker of the mineralocorticoid receptor (MR), approved for the treatment of hypertension in Japan and licensed to Daiichi Sankyo Company, Limited (Daiichi Sankyo). Basis of Consolidation The accompanying Condensed Consolidated Financial Statements include the accounts of Exelixis and those of our wholly-owned subsidiaries. These entities’ functional currency is the U.S. dollar. All intercompany balances and transactions have been eliminated. Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the U.S. for interim financial information and pursuant to Form 10-Q and Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. In our opinion, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation of our financial statements for the periods presented have been included. We have adopted a 52- or 53-week fiscal year policy that generally ends on the Friday closest to December 31 st . Fiscal year 2019, which is a 53-week fiscal year, will end on January 3, 2020 and fiscal year 2018, which was a 52-week fiscal year, ended on December 28, 2018. For convenience, references in this report as of and for the fiscal periods ended September 27, 2019, June 28, 2019, September 28, 2018 and June 29, 2018, and as of and for the fiscal years ending January 3, 2020, and ended December 28, 2018 and December 29, 2017, are indicated as being as of and for the periods ended September 30, 2019, June 30, 2019, September 30, 2018 and June 30, 2018 and the years ending December 31, 2019, and ended December 31, 2018 and December 31, 2017, respectively. Similarly, references in this report to the first day of the fiscal year ended January 3, 2020 are indicated as being as of January 1, 2019 and the first day of the fiscal quarter ended September 27, 2019 are indicated as being as of July 1, 2019. Operating results for the three and nine months ended September 30, 2019 are not necessarily indicative of the results that may be expected for the year ending December 31, 2019 or for any future period. The accompanying Condensed Consolidated Financial Statements and Notes thereto should be read in conjunction with our Consolidated Financial Statements and Notes thereto for the year ended December 31, 2018 , included in our Annual Report on Form 10-K filed with the SEC on February 22, 2019 . Segment Information We operate in one business segment that focuses on the discovery, development and commercialization of new medicines for difficult-to-treat cancers . Our Chief Executive Officer, as the chief operating decision-maker, manages and allocates resources to our operations on a total consolidated basis. Consistent with this decision-making process, our Chief Executive Officer uses consolidated, single-segment financial information for purposes of evaluating performance, forecasting future period financial results, allocating resources and setting incentive targets. All of our long-lived assets are located in the U.S. See “Note 2. Revenues” for enterprise-wide disclosures about product sales, revenues from major customers and revenues by geographic region. Use of Estimates The preparation of the accompanying Condensed Consolidated Financial Statements conforms to accounting principles generally accepted in the U.S., which requires management to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, equity, revenues and expenses, and related disclosures. On an ongoing basis, management evaluates its estimates including, but not limited to: those related to revenue recognition, including determining the nature and timing of satisfaction of performance obligations, and determining the standalone selling price of performance obligations, and variable consideration such as rebates, chargebacks, sales returns, sales allowances, and milestone payments included in collaboration arrangements; the amounts of revenues and expenses under our profit and loss sharing agreement; the recoverability of inventory; the amounts of operating lease right-of-use assets and lease liabilities; the amounts of deferred tax assets and liabilities including the related valuation allowance; the accrual for certain liabilities including accrued clinical trial liabilities; and valuations of equity awards used to determine stock-based compensation, including certain awards with vesting subject to market or performance conditions. We base our estimates on historical experience and on various other market-specific and other relevant assumptions that we believe 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 sources. Actual results could differ materially from those estimates. Recently Adopted Accounting Pronouncements On July 1, 2019, we adopted ASU No. 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (ASU 2018-15). ASU 2018-15 requires a customer in a hosting arrangement that is a service contract to follow the guidance in Accounting Standards Codification (ASC) Subtopic 350-40 to determine which implementation costs to capitalize as an asset related to the service contract and which costs to expense and requires us to expense the capitalized implementation costs over the term of the hosting arrangement, which includes reasonably certain renewals. ASU 2018-15 was adopted using the prospective transition method in the accompanying Condensed Consolidated Financial Statements. The adoption of ASU 2018-15 did not have a material impact on our Condensed Consolidated Financial Statements. On January 1, 2019, we adopted ASU 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220) (ASU 2018-02). There was no financial impact from the adoption of ASU 2018-02 and we did not make an election to reclassify the income tax effects of the Tax Cuts and Jobs Act of 2017 from Accumulated other comprehensive income (loss) to Accumulated deficit. In connection with the adoption of ASU 2018-02, we have adopted the individual unit of account approach for releasing income tax effects from Accumulated other comprehensive income (loss) . On January 1, 2019, we also adopted ASU 2017-08 , Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20) (ASU 2017-08). ASU 2017-08 shortens the amortization period for certain callable debt securities held at a premium. Specifically, ASU 2017-08 requires the premium to be amortized to the earliest call date. ASU 2017-08 does not require an accounting change for securities held at a discount; the discount continues to be amortized to maturity. The financial impact from the adoption of ASU 2017-08 was nominal. Recent Accounting Pronouncements Not Yet Adopted In November 2018, the Financial Accounting Standards Board (FASB) issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 (ASU 2018-18). ASU 2018-18 clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under Topic 606 when the counterparty is a customer for a distinct good or service (i.e. a unit of account). For units of account that are in the scope of Topic 606, all of the guidance in Topic 606 should be applied, including the guidance on recognition, measurement, presentation and disclosure. ASU 2018-18 also adds a reference in ASC Topic 808, Collaborative Arrangements (Topic 808) to the unit of account guidance in Topic 606 and requires that it be applied only to assess whether transactions in a collaborative arrangement are in the scope of Topic 606. ASU 2018-18 will preclude entities from presenting amounts related to transactions with a counterparty in a collaborative arrangement that is not a customer as revenue from contracts with customers. ASU 2018-18 is effective for us for all interim and annual reporting periods beginning after December 15, 2019. Early adoption is permitted. We are in the process of assessing the impact of ASU 2018-18 on our Condensed Consolidated Financial Statements. In January 2017, the FASB issued ASU No. 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04) . ASU 2017-04 eliminated Step 2 from the goodwill impairment test. Instead, under the amendments in ASU 2017-04, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. Additionally, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. ASU 2017-04 is effective for all interim and annual reporting periods beginning after December 15, 2019. Early adoption is permitted. We do not expect the adoption of ASU 2017-04 to have a material impact on our Condensed Consolidated Financial Statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326) (ASU 2016-13) . ASU 2016-13 implements an impairment model, known as the current expected credit loss model that is based on expected losses rather than incurred losses. Under the new guidance, an entity will recognize as an allowance its estimate of expected credit losses. 2016-13 is effective for all interim and annual reporting periods beginning after December 15, 2019. Early adoption is permitted. We do not expect the adoption of ASU 2016-13 to have a material impact on our Condensed Consolidated Financial Statements.

Revenues

Revenues	9 Months Ended
	Sep. 27, 2019
Revenue from Contract with Customer [Abstract]
REVENUES	REVENUES Revenues by disaggregated category were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Product revenues: Gross product revenues $ 239,916 $ 193,356 $ 704,084 $ 525,438 Discounts and allowances (48,148 ) (30,410 ) (139,060 ) (82,384 ) Net product revenues 191,768 162,946 565,024 443,054 Collaboration revenues: License revenues (1) 68,035 51,323 128,937 152,261 Research and development services revenues (2) 12,988 10,560 35,814 27,464 Other collaboration revenues (3) (1,088 ) 568 (2,310 ) 2,445 Total collaboration revenues 79,935 62,451 162,441 182,170 Total revenues $ 271,703 $ 225,397 $ 727,465 $ 625,224 ____________________ (1) License revenues included the recognition of the portion of milestones allocated to the transfer of intellectual property licenses for which it had become probable in the current period that the milestone would be achieved and a significant revenue reversal would not occur, as well as royalty revenues from Ipsen Pharma SAS (Ipsen), Genentech and Daiichi Sankyo. (2) Research and development services revenues included the recognition of deferred revenue for the portion of upfront and milestone payments that have been allocated to research and development services performance obligations, as well as development cost reimbursements earned on our collaboration agreements. (3) Other collaboration revenues included the profit on the U.S. commercialization of COTELLIC from Genentech and revenues on product supply services provided to Ipsen and Takeda Pharmaceutical Company Ltd. (Takeda), which were offset by the 3% royalty we are required to pay GlaxoSmithKline (GSK) on the net sales by Ipsen of any product incorporating cabozantinib. Net product revenues, License revenues and Research and development services revenues were recorded in accordance with Topic 606 for all periods presented. Net product revenues and License revenues related to goods and intellectual property licenses transferred at a point in time and Research and development services revenues related to services performed over time. Other collaboration revenues, which included the p rofit on the U.S. commercialization of COTELLIC and net losses on product supply services, were recorded in accordance with Topic 808 for all periods presented . Net product revenues disaggregated by product were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 CABOMETYX $ 187,410 $ 158,262 $ 552,315 $ 428,317 COMETRIQ 4,358 4,684 12,709 14,737 Net product revenues $ 191,768 $ 162,946 $ 565,024 $ 443,054 Total revenues disaggregated by significant customer were as follows (dollars in thousands): Three Months Ended September 30, 2019 2018 Dollars Percent of Total Dollars Percent of Total Ipsen $ 76,016 28 % $ 57,186 25 % Caremark L.L.C. 35,703 13 % 30,707 14 % Affiliates of McKesson Corporation 31,901 12 % 26,597 12 % Affiliates of AmerisourceBergen Corporation 25,235 9 % 17,232 8 % Others, individually less than 10% of Total revenues for all periods presented 102,848 38 % 93,675 41 % Total revenues $ 271,703 100 % $ 225,397 100 % Nine Months Ended September 30, 2019 2018 Dollars Percent of Total Dollars Percent of Total Ipsen $ 120,133 17 % $ 145,038 23 % Caremark L.L.C. 105,638 15 % 83,516 13 % Affiliates of McKesson Corporation 88,496 12 % 71,249 11 % Affiliates of AmerisourceBergen Corporation 70,503 10 % 49,995 8 % Others, individually less than 10% of Total revenues for all periods presented 342,695 46 % 275,426 45 % Total revenues $ 727,465 100 % $ 625,224 100 % Total revenues disaggregated by geographic region were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 U.S. $ 194,484 $ 166,270 $ 572,957 $ 453,342 Europe 76,017 57,186 120,134 145,038 Japan 1,202 1,941 34,374 26,844 Total revenues $ 271,703 $ 225,397 $ 727,465 $ 625,224 Net product revenues are attributed to geographic region based on the ship-to location. Collaboration revenues are attributed to geographic region based on the location of our collaboration partners’ headquarters. Product Sales Discounts and Allowances The activities and ending reserve balances for each significant category of discounts and allowances (which constitute variable consideration) were as follows (in thousands): Chargebacks and Discounts for Prompt Payment Other Customer Credits/Fees and Co-pay Assistance Rebates Total Balance at December 31, 2018 $ 2,322 $ 3,038 $ 11,916 $ 17,276 Provision related to sales made in: Current period 92,769 11,190 35,422 139,381 Prior periods (130 ) (106 ) (85 ) (321 ) Payments and customer credits issued (92,317 ) (11,466 ) (33,127 ) (136,910 ) Balance at September 30, 2019 $ 2,644 $ 2,656 $ 14,126 $ 19,426 Chargebacks and discounts for prompt payment are recorded as a reduction of trade receivables and the remaining reserve balances are classified as Other current liabilities in the accompanying Condensed Consolidated Balance Sheets. Contract Assets and Liabilities We receive payments from our licensees based on billing schedules established in each contract. Amounts are recorded as accounts receivable when our right to consideration is unconditional. We may also recognize revenue in advance of the contractual billing schedule and such amounts are recorded as unbilled collaboration revenue when recognized. Unbilled collaboration revenue was zero as of both September 30, 2019 and December 31, 2018 . Upfront and milestone payments may require deferral of revenue recognition to a future period until we perform our obligations under these arrangements and are recorded as deferred revenue upon receipt or when due. Deferred revenue was $15.4 million and $15.9 million as of September 30, 2019 and December 31, 2018 , respectively. The amount of revenues recognized during the nine months ended September 30, 2019 and 2018 that were included in the beginning deferred revenue balance as of December 31, 2018 and December 31, 2017 was $2.7 million and $6.1 million , respectively During the three and nine months ended September 30, 2019 , we recognized $67.7 million and $129.0 million , respectively, in revenues under Topic 606 for performance obligations satisfied in previous periods as compared to $48.2 million and $151.8 million during the same periods in 2018. Such revenues primarily related to milestone and royalty payments allocated to our license performance obligations of our collaborations with Ipsen, Takeda and Daiichi Sankyo.

Collaboration Agreements

Collaboration Agreements	9 Months Ended
	Sep. 27, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
COLLABORATION AGREEMENTS	COLLABORATION AGREEMENTS We have established multiple collaborations with leading pharmaceutical companies for the commercialization and further development of cabozantinib, as well as with smaller, discovery-focused biotechnology companies to expand our product pipeline. Additionally, in line with our business strategy prior to the commercialization of our first product, COMETRIQ, we entered into other collaborations with leading pharmaceutical companies including Genentech, Daiichi Sankyo and Bristol-Myers Squibb Company for other compounds and programs in our portfolio. See “Note 3. Collaboration Agreements” to our Consolidated Financial Statements included in our Annual Report on Form 10-K for the year ended December 31, 2018 for a description of each of our collaboration agreements. Under these collaborations, we are generally entitled to receive milestone and royalty payments, and for certain collaborations, payments for product supply services, development cost reimbursements, and/or profit-sharing payments. See “Note 2. Revenues” for information on collaboration revenues recognized during the three and nine months ended September 30, 2019 and 2018 . Commercial Collaborations Ipsen Collaboration In February 2016, we entered into a collaboration and license agreement with Ipsen for the commercialization and further development of cabozantinib. Pursuant to the terms of the collaboration agreement, Ipsen received exclusive commercialization rights for current and potential future cabozantinib indications outside of the U.S., Canada and Japan. The collaboration agreement was subsequently amended on three occasions, including in December 2016 to include commercialization rights in Canada. We have also agreed to collaborate with Ipsen on the development of cabozantinib for current and potential future indications. Collaboration revenues under the collaboration agreement with Ipsen were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Ipsen collaboration revenues $ 76,016 $ 57,186 $ 120,133 $ 145,038 As of September 30, 2019 , $47.1 million of the transaction price allocated to our research and development services performance obligation had not been satisfied. As of September 30, 2019 , the net contract liability for the collaboration agreement with Ipsen was $7.2 million which was included in the Long-term portion of deferred revenue in the accompanying Condensed Consolidated Balance Sheets. Takeda Collaboration In January 2017, we entered into a collaboration and license agreement with Takeda. Pursuant to this collaboration agreement, Takeda has exclusive commercialization rights for current and potential future cabozantinib indications in Japan, and the parties have agreed to collaborate on the clinical development of cabozantinib in Japan. The collaboration agreement was subsequently amended in March 2018 and April 2019. The second amendment to the collaboration agreement with Takeda, which was executed on April 29, 2019 and became effective on May 7, 2019 (the Amendment), among other things, reduced the amount of reimbursements we will receive from Takeda for costs associated with our required global pharmacovigilance activities and limits those reimbursements to $1.0 million per year. It also increased the total potential development, regulatory and first-sale milestone payments to be paid to us by Takeda for second-line RCC , first-line RCC and second-line HCC by $12.0 million to $102.0 million , including an increase from $10.0 million to $16.0 million for the milestone we received for the April 2019 submission of a regulatory application for cabozantinib as a treatment for patients with advanced RCC to the Japanese Ministry of Health, Labour and Welfare (MHLW) . We continue to be eligible to receive additional development, regulatory and first-sale milestone payments for other potential future indications. The Amendment also increased the amount of Takeda’s total potential commercial milestones by $6.0 million to $89.0 million . We continue to be eligible to receive royalties on net sales of cabozantinib in Japan. Collaboration revenues under the collaboration agreement with Takeda were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Takeda collaboration revenues $ 1,187 $ 1,940 $ 14,245 $ 6,843 As of September 30, 2019 , $18.7 million of the transaction price allocated to our research and development services performance obligation had not been satisfied. As of September 30, 2019 , the net contract liability for the collaboration agreement with Takeda was $8.2 million which was included in the Long-term portion of deferred revenue in the accompanying Condensed Consolidated Balance Sheets. Genentech Collaboration In December 2006, we out-licensed the development and commercialization of cobimetinib to Genentech pursuant to a worldwide collaboration agreement. Under the terms of the collaboration agreement, we developed cobimetinib through the determination of the maximum tolerated dose in a phase 1 clinical trial, and Genentech had the option to co-develop cobimetinib, an option that Genentech exercised, and in March 2009, we granted to Genentech an exclusive worldwide revenue-bearing license to cobimetinib, at which point Genentech became responsible for completing the phase 1 clinical trial and the subsequent clinical development. In November 2015, the U.S. Food and Drug Administration (FDA) approved cobimetinib, under the brand name COTELLIC, in combination with Genentech’s Zelboraf (vemurafenib) as a treatment for patients with BRAF V600E or V600K mutation-positive advanced melanoma. COTELLIC in combination with Zelboraf has also been approved in the European Union and multiple additional countries for use in the same indication. Profits on U.S. commercialization and Royalty revenues on ex-U.S. sales were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Profits on U.S. commercialization $ 1,102 $ 1,935 $ 3,507 $ 6,004 Royalty revenues on ex-U.S. sales $ 1,614 $ 1,390 $ 4,426 $ 4,285 Daiichi Sankyo In March 2006, we entered into a collaboration agreement with Daiichi Sankyo pursuant to which we granted to Daiichi Sankyo an exclusive, worldwide license to certain intellectual property primarily relating to compounds that modulate MR, including esaxerenone, an oral, non-steroidal, selective MR antagonist. Daiichi Sankyo was responsible for all further preclinical and clinical development, regulatory, manufacturing and commercialization activities for the compounds. In January 2019, the Japanese MHLW approved esaxerenone, under the brand name MINNEBRO, as a treatment for patients with hypertension and in May 2019, Daiichi Sankyo had its first commercial sale of MINNEBRO . As a result of the launch, we received a $20.0 million milestone payment from Daiichi Sankyo in June 2019. We are eligible for low double-digit royalties on sales of MINNEBRO. In addition, pursuant to a license agreement we entered into with Ligand Pharmaceuticals, Inc. (Ligand), we are required to pay a royalty of 0.5% to Ligand on net sales of MINNEBRO. Collaboration revenues under the collaboration agreement with Daiichi Sankyo were as follows (in thousands): Nine Months Ended September 30, 2019 2018 Daiichi Sankyo collaboration revenues $ 20,130 $ 20,000 Such collaboration revenues were nominal or zero for the three months ended September 30, 2019 and 2018. Iconic Therapeutics, Inc. (Iconic) Collaboration In May 2019, we entered into an exclusive option and license agreement with Iconic. Under the terms of the agreement, we gained an exclusive option to license ICON-2, Iconic’s lead oncology antibody-drug conjugate program, in exchange for an upfront payment to Iconic of $7.5 million and a commitment for preclinical development funding. As of September 30, 2019 , we accrued $6.6 million for the preclinical development funding commitment. Both the upfront payment and the accrual for the preclinical development funding commitment were included in Research and development expenses in the accompanying Condensed Consolidated Statements of Income. If we exercise the option, we would be required to make an option exercise fee payment of $20.0 million to Iconic, we would assume responsibilities for all subsequent clinical development and commercialization activities, and Iconic would become eligible for up to $190.6 million in potential development, regulatory and first-sale milestone payments, $262.5 million in potential commercial milestone payments, as well as royalties on potential sales. Aurigene Discovery Technologies Limited (Aurigene) Collaboration In July 2019, we entered into an exclusive collaboration, option and license agreement with Aurigene, and India-based biotechnology company focused on oncology and inflammatory disorders, to in-license as many as six programs. Under the terms of the agreement, we made an upfront payment of $10.0 million for exclusive options to license three preexisting programs. In addition, we and Aurigene selected three additional Aurigene-led drug discovery programs on mutually agreed upon targets, in exchange for additional option payments totaling $7.5 million . We are also responsible for up to $32.6 million in research funding for the discovery and preclinical development work on these programs. As of September 30, 2019 , we accrued $1.3 million for the discovery and preclinical development funding commitment. For each option we decide to exercise, we would be required to pay an exercise fee of either $10.0 million or $12.0 million , depending on the program, and would assume responsibilities for all subsequent clinical development, commercialization and global manufacturing of that program. Aurigene would then become eligible for up to $148.8 million per program in potential development and regulatory milestone payments, $280.0 million per program in potential commercial milestone payments, as well as royalties on potential sales. Under the terms of the agreement, Aurigene retains limited development and commercial rights for India and Russia. GSK In October 2002, we established a product development and commercialization collaboration agreement with GSK. Under the terms of the collaboration agreement, GSK had the right to choose cabozantinib for further development and commercialization, but notified us in October 2008 that it had waived its right to select the compound for such activities. Although the collaboration agreement was terminated in December 2014, we continue to be required to pay a 3% royalty to GSK on the net sales of any product incorporating cabozantinib by us and our collaboration partners. Royalties accruing to GSK in connection with the sales of cabozantinib are included in Cost of goods sold for sales by us and as a reduction of Collaboration revenues for sales by Ipsen. Such royalties accruing to GSK were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Royalties accruing to GSK $ 7,964 $ 6,268 $ 23,079 $ 17,021

Cash and Investments

Cash and Investments	9 Months Ended
	Sep. 27, 2019
Investments, Debt and Equity Securities [Abstract]
CASH AND INVESTMENTS	CASH AND INVESTMENTS Cash, Cash Equivalents and Restricted Cash A reconciliation of Cash, cash equivalents, and restricted cash reported within our Condensed Consolidated Balance Sheets to the amount reported within the accompanying Condensed Consolidated Statements of Cash Flows was as follows (in thousands): September 30, 2019 December 31, 2018 September 30, 2018 December 31, 2017 Cash and cash equivalents $ 242,317 $ 314,775 $ 353,623 $ 183,164 Restricted cash included in short-term restricted cash and investments — — 504 504 Restricted cash included in long-term restricted cash and investments 1,000 1,100 1,100 4,646 Cash, cash equivalents, and restricted cash as reported within the accompanying Condensed Consolidated Statements of Cash Flows $ 243,317 $ 315,875 $ 355,227 $ 188,314 Restricted cash includes certificates of deposit used to collateralize letters of credit and, in prior periods, a purchasing card program. Cash and Investments Cash and investments by security type were as follows (in thousands): September 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Investments available-for-sale: Money market funds $ 26,641 $ — $ — $ 26,641 Commercial paper 332,239 — — 332,239 Corporate bonds 703,325 3,549 (67 ) 706,807 U.S. Treasury and government sponsored enterprises 152,531 143 (24 ) 152,650 Total investments available-for-sale 1,214,736 3,692 (91 ) 1,218,337 Cash and restricted cash 901 — — 901 Certificates of deposit 29,189 3 — 29,192 Total cash and investments $ 1,244,826 $ 3,695 $ (91 ) $ 1,248,430 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Investments available-for-sale: Money market funds $ 47,744 $ — $ — $ 47,744 Commercial paper 381,134 — (1 ) 381,133 Corporate bonds 344,741 180 (857 ) 344,064 U.S. Treasury and government sponsored enterprises 55,224 2 (25 ) 55,201 Total investments available-for-sale 828,843 182 (883 ) 828,142 Cash and restricted cash 6,883 — — 6,883 Certificates of deposit 16,596 — — 16,596 Total cash and investments $ 852,322 $ 182 $ (883 ) $ 851,621 Gains and losses on the sales of investments available-for-sale were nominal during the three and nine months ended September 30, 2019 and 2018 . The fair value and gross unrealized losses on investments available-for-sale in an unrealized loss position were as follows (in thousands): September 30, 2019 In an Unrealized Loss Position Less than 12 Months In an Unrealized Loss Position 12 Months or Greater Total Fair Value Gross Fair Value Gross Fair Value Gross Corporate bonds $ 73,064 $ (66 ) $ 4,398 $ (1 ) $ 77,462 $ (67 ) U.S. Treasury and government sponsored enterprises 46,744 (24 ) — — 46,744 (24 ) Total $ 119,808 $ (90 ) $ 4,398 $ (1 ) $ 124,206 $ (91 ) December 31, 2018 In an Unrealized Loss Position Less than 12 Months In an Unrealized Loss Position 12 Months or Greater Total Fair Value Gross Fair Value Gross Fair Value Gross Corporate bonds $ 236,162 $ (606 ) $ 39,627 $ (251 ) $ 275,789 $ (857 ) U.S. Treasury and government sponsored enterprises 28,105 (16 ) 9,182 (9 ) 37,287 (25 ) Commercial paper 7,091 (1 ) — — 7,091 (1 ) Total $ 271,358 $ (623 ) $ 48,809 $ (260 ) $ 320,167 $ (883 ) There were 43 and 199 investments in an unrealized loss position as of September 30, 2019 and December 31, 2018 , respectively. During the three and nine months ended September 30, 2019 and 2018 we did no t record any other-than-temporary impairment charges on our available-for-sale securities. Based upon our quarterly impairment review, we determined that the unrealized losses were not attributed to credit risk, but were primarily associated with changes in interest rates. Based on the scheduled maturities of our investments and our determination that it was more likely than not that we will hold these investments for a period of time sufficient for a recovery of our cost basis, we concluded that the unrealized losses in our investment securities were not other-than-temporary. The fair value of investments available-for-sale by contractual maturity were as follows (in thousands): September 30, December 31, 2018 Maturing in one year or less $ 743,768 $ 674,455 Maturing after one year through five years 474,569 153,687 Total investments available-for-sale $ 1,218,337 $ 828,142 Related Party Transactions BlackRock, Inc. (BlackRock), a global provider of investment, advisory and risk management solutions, reported that as of December 31, 2018 , the most recent date for which they reported ownership data, their beneficial ownership was more than 10% of our outstanding common stock. BlackRock manages a portion of our cash and investments portfolio. As of September 30, 2019 and December 31, 2018 , respectively, the fair value of cash and investments managed by BlackRock was $470.8 million and $298.5 million , which included $1.9 million and $3.0 million invested in the BlackRock Liquidity Money Market Fund. As of September 30, 2019 , we also had a $9.0 million payable to BlackRock for unsettled trades that was included in Other current liabilities in the accompanying Condensed Consolidated Balance Sheets. We incurred $0.2 million in fees for BlackRock advisory services performed during the nine months ended September 30, 2019 .

Inventory

Inventory	9 Months Ended
	Sep. 27, 2019
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY Inventory consisted of the following (in thousands): September 30, December 31, 2018 Raw materials $ 1,906 $ 1,922 Work in process 11,035 6,170 Finished goods 7,311 3,836 Total $ 20,252 $ 11,928 Balance Sheet classification: Current portion included in Inventory $ 13,366 $ 9,838 Long-term portion included in Other long-term assets 6,886 2,090 Total $ 20,252 $ 11,928 Write-downs related to excess and expiring inventory are charged to Cost of goods sold or the cost of supplied product included in Collaboration revenues. Such write-downs were $0.4 million and $0.8 million for the nine months ended September 30, 2019 and 2018 , respectively. Inventory not expected to be used in production or sold in the next 12 months is classified as Other long-term assets in the accompanying Condensed Consolidated Balance Sheets. As of both September 30, 2019 and December 31, 2018 , the long-term portion of inventory consisted of portions of our raw materials and finished goods, and as of September 30, 2019 , also a portion of our work in process.

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 27, 2019
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT Property and equipment consisted of the following (in thousands): September 30, December 31, Leasehold improvements $ 33,769 $ 33,941 Computer equipment and software 17,017 15,022 Furniture and fixtures 13,053 12,709 Laboratory equipment 8,408 5,668 Construction in progress 617 866 72,864 68,206 Less: accumulated depreciation and amortization (23,397 ) (17,309 ) Property and equipment, net $ 49,467 $ 50,897 Depreciation expense was $2.1 million and $6.1 million for the three and nine months ended September 30, 2019 , respectively, as compared to $1.7 million and $2.9 million and for the comparable periods in 2018

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 27, 2019
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION We allocated the stock-based compensation expense for our equity incentive plans and our 2000 Employee Stock Purchase Plan (ESPP) as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Research and development $ 4,301 $ 3,169 $ 13,745 $ 9,102 Selling, general and administrative 8,838 6,573 27,002 19,228 Total stock-based compensation $ 13,139 $ 9,742 $ 40,747 $ 28,330 We have several equity incentive plans under which we have granted stock options and restricted stock units (RSUs) to employees and directors. At September 30, 2019 , 6,024,995 shares were available for grant under our equity incentive plans. We used a Monte Carlo simulation pricing model to value stock options that include market vesting conditions and a Black-Scholes Merton option pricing model to value other stock options and ESPP purchases. The weighted average grant-date fair value per share of stock options and ESPP purchases were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Stock options $ 7.71 $ 8.67 $ 8.57 $ 9.13 ESPP $ 5.39 $ 6.19 $ 4.93 $ 6.96 The grant-date fair value of stock option grants and ESPP purchases was estimated using the following assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Stock options: Risk-free interest rate 1.57 % 2.91 % 1.82 % 2.83 % Dividend yield — % — % — % — % Volatility 48 % 55 % 48 % 55 % Expected life 4.0 years 4.4 years 4.4 years 4.4 years ESPP: Risk-free interest rate 2.09 % 2.11 % 2.34 % 1.74 % Dividend yield — % — % — % — % Volatility 43 % 51 % 52 % 52 % Expected life 6 months 6 months 6 months 6 months We considered our implied volatility and our historical volatility in developing our estimates of expected volatility. The assumptions for the expected life of stock options were based on historical exercise patterns and post-vesting termination behavior. The risk-free interest rate is based on U.S. Treasury rates with the same or similar term as the underlying award. Our dividend rate is based on historical experience and our investors’ current expectations. The fair value of RSUs was based on the closing price of the underlying common stock on the date of grant. Activity for stock options during the nine months ended September 30, 2019 was as follows (dollars in thousands , except per share amounts): Shares Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term Aggregate Intrinsic Value Options outstanding at December 31, 2018 22,674,062 $ 8.71 Granted 1,042,286 $ 20.81 Exercised (3,042,201 ) $ 4.94 Forfeited (160,241 ) $ 16.76 Expired (35,045 ) $ 23.41 Options outstanding at September 30, 2019 20,478,861 $ 9.80 3.4 years $ 186,407 Exercisable at September 30, 2019 15,860,131 $ 7.02 2.8 years $ 181,542 As of September 30, 2019 , there was $38.0 million of unrecognized compensation expense related to our unvested stock options. The compensation expense for the unvested stock options will be recognized over a weighted-average period of 2.3 years . Activity for RSUs during the nine months ended September 30, 2019 was as follows (dollars in thousands , except per share amounts): Shares Weighted Average Grant Date Fair Value Per Share Weighted Average Remaining Contractual Term Aggregate Intrinsic Value RSUs outstanding at December 31, 2018 4,857,334 $ 18.42 Awarded 5,635,362 $ 19.54 Vested and released (484,731 ) $ 12.33 Forfeited (258,142 ) $ 18.47 RSUs outstanding at September 30, 2019 9,749,823 $ 19.37 2.2 years $ 175,448 As of September 30, 2019 , there was $166.0 million of unrecognized compensation expense related to our unvested RSUs, including those RSUs granted in September 2018 and September 2019 that will vest upon the achievement of specific performance targets (PSUs) described below. The compensation expense for the unvested RSUs will be recognized over a weighted-average period of 2.8 years . During 2019, in connection with our long-term incentive compensation program, we awarded 1,926,605 RSUs (the target amount) that will vest upon the achievement of a performance target related to a product approval by the FDA (the 2019 PSUs); employees may earn 150% of the target amount , or an additional 963,136 shares relative to the target amount, if the performance target is achieved before December 31, 2020 and may earn the full 200% of the target amount, or up to an additional 1,926,605 shares relative to the target amount, if we receive a second product approval. During 2018 we awarded 693,131 RSUs that will vest upon the achievement of certain product revenue, late-stage clinical development and pipeline expansion performance targets (the 2018 PSUs). The 2018 PSUs and 2019 PSUs were designed to drive the performance of our management team and employees toward the achievement of key corporate objectives and will be forfeited if the performance targets are not met by December 31, 2021. Expense recognition for PSUs commences when it is determined that attainment of the performance target is probable. During the quarter ended June 30, 2019 , we achieved one of the two product revenue related performance targets for 114,843 of the 2018 PSUs and determined that it was probable that we would achieve the second product revenue related performance target for 172,272 additional 2018 PSUs. D uring the quarter ended September 30, 2019, the second product revenue related performance target of the 2018 PSUs was achieved . Those 2018 PSUs will vest over various dates through February 2021. We recognized $0.9 million and $3.5 million in compensation expense related to those 2018 PSUs during the three and nine months ended September 30, 2019 , respectively; the remaining unrecognized compensation expense for those 2018 PSUs was $1.7 million as of September 30, 2019 . The total unrecognized compensation expense for both the 2019 PSUs and the remaining 2018 PSUs for which we have not yet determined that attainment of the performance target is probable was $82.4 million as of September 30, 2019 .

Income Taxes

Income Taxes	9 Months Ended
	Sep. 27, 2019
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES Our effective income tax rate was 20.5% and 19.4% during the three and nine months ended September 30, 2019 , respectively, as compared to 1.8% and 1.7% during the three and nine months ended September 30, 2018 , respectively. The Provision for income taxes relating to our pre-tax income for the three and nine months ended September 30, 2018 was largely offset by a valuation allowance against our net operating loss carryforwards and other deferred tax assets. At December 31, 2018, we released substantially all of our valuation allowance against our deferred tax assets, after we determined that it was more likely than not that these deferred tax assets would be realized. The effective tax rate for the three and nine months ended September 30, 2019 differed from the U.S. federal statutory rate of 21%

Net Income Per Share

Net Income Per Share	9 Months Ended
	Sep. 27, 2019
Earnings Per Share [Abstract]
NET INCOME PER SHARE	NET INCOME PER SHARE The basic and diluted net income per share were computed as follows (in thousands, except per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Numerator: Net income $ 97,452 $ 126,630 $ 252,269 $ 329,981 Denominator: Weighted-average shares of common stock outstanding used in computing basic net income per share 303,268 298,416 301,999 297,700 Dilutive securities 12,185 13,930 13,047 15,500 Weighted-average shares of common stock outstanding and dilutive securities used in computing diluted net income per share 315,453 312,346 315,046 313,200 Net income per share, basic $ 0.32 $ 0.42 $ 0.84 $ 1.11 Net income per share, diluted $ 0.31 $ 0.41 $ 0.80 $ 1.05 Dilutive securities include outstanding stock options, unvested RSUs and ESPP contributions. Potential shares of common stock not included in the computation of diluted net income per share because to do so would be anti-dilutive, were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Potentially dilutive securities 6,153 5,687 5,740 2,938

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 27, 2019
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The classifications within the fair value hierarchy of our financial assets that were measured and recorded at fair value on a recurring basis were as follows (in thousands): September 30, 2019 Level 1 Level 2 Total Money market funds $ 26,641 $ — $ 26,641 Commercial paper — 332,239 332,239 Corporate bonds — 706,807 706,807 U.S. Treasury and government sponsored enterprises — 152,650 152,650 Total investments available-for-sale 26,641 1,191,696 1,218,337 Certificates of deposit — 29,192 29,192 Total financial assets carried at fair value $ 26,641 $ 1,220,888 $ 1,247,529 December 31, 2018 Level 1 Level 2 Total Money market funds $ 47,744 $ — $ 47,744 Commercial paper — 381,133 381,133 Corporate bonds — 344,064 344,064 U.S. Treasury and government sponsored enterprises — 55,201 55,201 Total investments available-for-sale 47,744 780,398 828,142 Certificates of deposit — 16,596 16,596 Total financial assets carried at fair value $ 47,744 $ 796,994 $ 844,738 We did not have any financial liabilities measured and recorded at fair value on a recurring basis as of September 30, 2019 or December 31, 2018 . We did not have any financial assets or liabilities classified as Level 3 in the fair value hierarchy as of September 30, 2019 or December 31, 2018 . There were no transfers of financial assets or liabilities between Levels 1, 2 and 3 during the three and nine months ended September 30, 2019 or 2018 . When available, we value investments based on quoted prices for those financial instruments, which is a Level 1 input. Our remaining investments are valued using third-party pricing sources, which use observable market prices, interest rates and yield curves observable at commonly quoted intervals for similar assets as observable inputs for pricing, which is a Level 2 input. See “Note 11. Leases” for a description of the determination of the amount of operating lease liabilities. Our remaining financial assets and liabilities include cash and restricted cash, Trade receivables, net, Other receivables, Accounts payable, Accrued compensation and benefits, Accrued clinical trial liabilities, Accrued collaboration liabilities and Rebates and fees due to customers. Those financial assets and liabilities are carried at cost, which approximates their fair values.

Leases

Leases	9 Months Ended
	Sep. 27, 2019
Leases [Abstract]
LEASES	LEASES In May 2017, we entered into a Lease Agreement (the Lease) for our corporate headquarters located at 1851, 1801 and 1751 Harbor Bay Parkway, Alameda, California (the Initial Premises). The Lease was subsequently amended in October 2017, June 2018 and April 2019, resulting in the addition of the building located at 1601 Harbor Bay Parkway and increasing the leased space to an aggregate of 169,606 square feet (the Current Premises) as of September 30, 2019 . We have made certain tenant improvements to the space leased on the Initial Premises, for which we received $8.2 million in reimbursements in January 2019. The Lease’s initial term is through January 31, 2028. Rent payments began February 1, 2018, following the conclusion of a partial twelve-month rent abatement period. We have two five-year options to extend the Lease and a one-time option to terminate the Lease without cause on the last day of the 8 th year of the initial term (the Early Termination Right); none of these optional periods have been considered in the determination of the right-of-use asset or the lease liability for the Lease as we did not consider it reasonably certain that we would exercise any such options. The Lease further provides that we are obligated to pay the landlord certain variable costs, including taxes and operating expenses. The April 2019 amendment to the Lease (the Third Lease Amendment) provides, among other things, for the (i) expansion of the Initial Premises by 37,544 square feet of office facilities located at 1601 Harbor Bay Parkway, Alameda, California (the 1601 Expansion Space) and (ii) surrender of 2,703 square feet of office facilities located at 1751 Harbor Bay Parkway, Alameda, California (the 1751 Space). The term for the 1601 Expansion Space will run coterminous with the term of the Lease for the existing space. We have been provided an allowance of $1.7 million for tenant improvements to the 1601 Expansion Space. As of September 30, 2019 , we have surrendered the 1751 Space and we have taken possession of the 1601 Expansion Space, and accordingly we have adjusted our right-of-use asset and lease liability, and have begun to recognize lease costs for the Third Lease Amendment. The balance sheet classification of our lease liabilities were as follows (in thousands): September 30, December 31, 2018 Operating lease liabilities: Current portion included in Other current liabilities $ 2,695 $ 2,738 Long-term portion of lease liabilities 23,661 12,099 Total operating lease liabilities 26,356 14,837 Financing lease liabilities: Current portion included in Other current liabilities 50 49 Long-term portion of lease liabilities 44 79 Total financing lease liabilities 94 128 Total lease liabilities $ 26,450 $ 14,965 The components of lease costs for operating leases, which were included in Selling, general and administrative expenses in our Condensed Consolidated Statements of Income, were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Operating lease cost $ 692 $ 1,614 $ 1,768 $ 3,587 Variable lease cost 274 363 654 1,366 Total lease costs $ 966 $ 1,977 $ 2,422 $ 4,953 Cash paid for amounts included in the measurement of lease liabilities for the nine months ended September 30, 2019 was $2.1 million and was included in Net cash provided by operating activities in our Condensed Consolidated Statements of Cash Flows. As of September 30, 2019 , the maturities of our operating lease liabilities were as follows (in thousands): Remainder of 2019 $ 745 Years ending December 31, 2020 3,625 2021 3,731 2022 3,852 2023 3,959 Thereafter 17,444 Total lease payments 33,356 Less: Present value adjustment (5,258 ) Tenant improvement reimbursements (1) (1,742 ) Operating lease liabilities $ 26,356 ____________________ (1) Represents anticipated tenant improvement reimbursements applicable to the portion of the 1601 Expansion Space. Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, we use our incremental borrowing rate. The weighted average discount rate used to determine the operating lease liability was 4.20% . As of September 30, 2019 , the weighted average remaining lease term is 8.3 years
LEASES	LEASES In May 2017, we entered into a Lease Agreement (the Lease) for our corporate headquarters located at 1851, 1801 and 1751 Harbor Bay Parkway, Alameda, California (the Initial Premises). The Lease was subsequently amended in October 2017, June 2018 and April 2019, resulting in the addition of the building located at 1601 Harbor Bay Parkway and increasing the leased space to an aggregate of 169,606 square feet (the Current Premises) as of September 30, 2019 . We have made certain tenant improvements to the space leased on the Initial Premises, for which we received $8.2 million in reimbursements in January 2019. The Lease’s initial term is through January 31, 2028. Rent payments began February 1, 2018, following the conclusion of a partial twelve-month rent abatement period. We have two five-year options to extend the Lease and a one-time option to terminate the Lease without cause on the last day of the 8 th year of the initial term (the Early Termination Right); none of these optional periods have been considered in the determination of the right-of-use asset or the lease liability for the Lease as we did not consider it reasonably certain that we would exercise any such options. The Lease further provides that we are obligated to pay the landlord certain variable costs, including taxes and operating expenses. The April 2019 amendment to the Lease (the Third Lease Amendment) provides, among other things, for the (i) expansion of the Initial Premises by 37,544 square feet of office facilities located at 1601 Harbor Bay Parkway, Alameda, California (the 1601 Expansion Space) and (ii) surrender of 2,703 square feet of office facilities located at 1751 Harbor Bay Parkway, Alameda, California (the 1751 Space). The term for the 1601 Expansion Space will run coterminous with the term of the Lease for the existing space. We have been provided an allowance of $1.7 million for tenant improvements to the 1601 Expansion Space. As of September 30, 2019 , we have surrendered the 1751 Space and we have taken possession of the 1601 Expansion Space, and accordingly we have adjusted our right-of-use asset and lease liability, and have begun to recognize lease costs for the Third Lease Amendment. The balance sheet classification of our lease liabilities were as follows (in thousands): September 30, December 31, 2018 Operating lease liabilities: Current portion included in Other current liabilities $ 2,695 $ 2,738 Long-term portion of lease liabilities 23,661 12,099 Total operating lease liabilities 26,356 14,837 Financing lease liabilities: Current portion included in Other current liabilities 50 49 Long-term portion of lease liabilities 44 79 Total financing lease liabilities 94 128 Total lease liabilities $ 26,450 $ 14,965 The components of lease costs for operating leases, which were included in Selling, general and administrative expenses in our Condensed Consolidated Statements of Income, were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Operating lease cost $ 692 $ 1,614 $ 1,768 $ 3,587 Variable lease cost 274 363 654 1,366 Total lease costs $ 966 $ 1,977 $ 2,422 $ 4,953 Cash paid for amounts included in the measurement of lease liabilities for the nine months ended September 30, 2019 was $2.1 million and was included in Net cash provided by operating activities in our Condensed Consolidated Statements of Cash Flows. As of September 30, 2019 , the maturities of our operating lease liabilities were as follows (in thousands): Remainder of 2019 $ 745 Years ending December 31, 2020 3,625 2021 3,731 2022 3,852 2023 3,959 Thereafter 17,444 Total lease payments 33,356 Less: Present value adjustment (5,258 ) Tenant improvement reimbursements (1) (1,742 ) Operating lease liabilities $ 26,356 ____________________ (1) Represents anticipated tenant improvement reimbursements applicable to the portion of the 1601 Expansion Space. Operating lease liabilities are based on the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, we use our incremental borrowing rate. The weighted average discount rate used to determine the operating lease liability was 4.20% . As of September 30, 2019 , the weighted average remaining lease term is 8.3 years

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 27, 2019
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	NOTE 12. SUBSEQUENT EVENTS Build to Suit Lease On October 25, 2019 , we entered into a build-to-suit Lease Agreement (the Build-to-Suit Lease) with Ernst Development Partners, Inc. (Ernst), for approximately 220,000 square feet of office space located in Alameda, California (the New Premises), adjacent to the Current Premises. The term of the Build-to-Suit Lease is for a period of 242 months (the Term), which will begin on the completion of the building and tenant improvements by Ernst. The Term is currently anticipated to begin on October 25, 2021 . The monthly base rent under the Build-to-Suit Lease will equal to a percentage of the total development costs incurred in connection with the development of the New Premises (excluding the cost of the tenant improvements in excess of the allowance provided by Ernst and any development costs we pay) and is currently estimated to be about $726,000 , subject to an annual increase of 3% during the Term. The monthly base rent will begin sixty days following commencement of the Term. We will also be responsible for paying operating expenses related to the New Premises. The Build-to-Suit Lease includes two five-year options to extend the term of the Build-to-Suit Lease, exercisable under certain conditions and at a market rate determined in accordance with the Build-to-Suit Lease. We have a one-time option to terminate the Build-to-Suit Lease without cause after the 180 th month of the Term, exercisable under certain conditions as described in the Build-to-Suit Lease and subject to a termination payment calculated in accordance with the Build-to-Suit Lease. See Part II, Item 5 of this Quarterly Report on Form 10-Q for more information about the Build to Suit Lease. Fourth Amendment to the Lease In the fourth quarter of 2019, Hillwood Enterprises, L.P. (Hillwood) is expected to purchase the project known as 1750 North Loop Road and 1601, 1701, 1751, 1801 and 1851 Harbor Bay Parkway, Alameda, California from Ascentris 105, LLC (the Purchase), which project includes the Current Premises. Effective upon the Purchase, Hillwood will become the landlord pursuant to the Lease. On August 30, 2019, we entered into an amendment to the Lease with Hillwood (the Fourth Lease Amendment), pursuant to which each of our rights and obligations are contingent upon the Purchase. Effective upon the Purchase, the Fourth Lease Amendment will provide for, among other things, the (i) expansion of the Current Premises by 59,335 square feet of laboratory facilities located at 1701 Harbor Bay Parkway, Alameda, California, (ii) extension of the Lease term through October 31, 2031 and (iii) elimination of the Early Termination Right. As of September 30, 2019, we have not yet recorded a right-of-use asset or lease liability for the Fourth Lease Amendment, and the remainder of the disclosures in this note do not reflect the impact of this amendment. See Part II, Item 5 of this Quarterly Report on Form 10-Q for more information about the Fourth Lease Amendment.

Organization and Summary of S_2

Organization and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 27, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Consolidation	Basis of Consolidation The accompanying Condensed Consolidated Financial Statements include the accounts of Exelixis and those of our wholly-owned subsidiaries. These entities’ functional currency is the U.S. dollar. All intercompany balances and transactions have been eliminated.
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the U.S. for interim financial information and pursuant to Form 10-Q and Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements. In our opinion, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation of our financial statements for the periods presented have been included.
Fiscal Period	We have adopted a 52- or 53-week fiscal year policy that generally ends on the Friday closest to December 31 st . Fiscal year 2019, which is a 53-week fiscal year, will end on January 3, 2020 and fiscal year 2018, which was a 52-week fiscal year, ended on December 28, 2018. For convenience, references in this report as of and for the fiscal periods ended September 27, 2019, June 28, 2019, September 28, 2018 and June 29, 2018, and as of and for the fiscal years ending January 3, 2020, and ended December 28, 2018 and December 29, 2017, are indicated as being as of and for the periods ended September 30, 2019, June 30, 2019, September 30, 2018 and June 30, 2018 and the years ending December 31, 2019, and ended December 31, 2018 and December 31, 2017, respectively. Similarly, references in this report to the first day of the fiscal year ended January 3, 2020 are indicated as being as of January 1, 2019 and the first day of the fiscal quarter ended September 27, 2019 are indicated as being as of July 1, 2019.
Segment Information	Segment Information We operate in one business segment that focuses on the discovery, development and commercialization of new medicines for difficult-to-treat cancers . Our Chief Executive Officer, as the chief operating decision-maker, manages and allocates resources to our operations on a total consolidated basis. Consistent with this decision-making process, our Chief Executive Officer uses consolidated, single-segment financial information for purposes of evaluating performance, forecasting future period financial results, allocating resources and setting incentive targets.
Use of Estimates	Use of Estimates The preparation of the accompanying Condensed Consolidated Financial Statements conforms to accounting principles generally accepted in the U.S., which requires management to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, equity, revenues and expenses, and related disclosures. On an ongoing basis, management evaluates its estimates including, but not limited to: those related to revenue recognition, including determining the nature and timing of satisfaction of performance obligations, and determining the standalone selling price of performance obligations, and variable consideration such as rebates, chargebacks, sales returns, sales allowances, and milestone payments included in collaboration arrangements; the amounts of revenues and expenses under our profit and loss sharing agreement; the recoverability of inventory; the amounts of operating lease right-of-use assets and lease liabilities; the amounts of deferred tax assets and liabilities including the related valuation allowance; the accrual for certain liabilities including accrued clinical trial liabilities; and valuations of equity awards used to determine stock-based compensation, including certain awards with vesting subject to market or performance conditions. We base our estimates on historical experience and on various other market-specific and other relevant assumptions that we believe 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 sources. Actual results could differ materially from those estimates.
Recently Adopted Accounting Pronouncements and Recent Accounting Pronouncements Not Yet Adopted	Recently Adopted Accounting Pronouncements On July 1, 2019, we adopted ASU No. 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (ASU 2018-15). ASU 2018-15 requires a customer in a hosting arrangement that is a service contract to follow the guidance in Accounting Standards Codification (ASC) Subtopic 350-40 to determine which implementation costs to capitalize as an asset related to the service contract and which costs to expense and requires us to expense the capitalized implementation costs over the term of the hosting arrangement, which includes reasonably certain renewals. ASU 2018-15 was adopted using the prospective transition method in the accompanying Condensed Consolidated Financial Statements. The adoption of ASU 2018-15 did not have a material impact on our Condensed Consolidated Financial Statements. On January 1, 2019, we adopted ASU 2018-02, Income Statement—Reporting Comprehensive Income (Topic 220) (ASU 2018-02). There was no financial impact from the adoption of ASU 2018-02 and we did not make an election to reclassify the income tax effects of the Tax Cuts and Jobs Act of 2017 from Accumulated other comprehensive income (loss) to Accumulated deficit. In connection with the adoption of ASU 2018-02, we have adopted the individual unit of account approach for releasing income tax effects from Accumulated other comprehensive income (loss) . On January 1, 2019, we also adopted ASU 2017-08 , Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20) (ASU 2017-08). ASU 2017-08 shortens the amortization period for certain callable debt securities held at a premium. Specifically, ASU 2017-08 requires the premium to be amortized to the earliest call date. ASU 2017-08 does not require an accounting change for securities held at a discount; the discount continues to be amortized to maturity. The financial impact from the adoption of ASU 2017-08 was nominal. Recent Accounting Pronouncements Not Yet Adopted In November 2018, the Financial Accounting Standards Board (FASB) issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 (ASU 2018-18). ASU 2018-18 clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under Topic 606 when the counterparty is a customer for a distinct good or service (i.e. a unit of account). For units of account that are in the scope of Topic 606, all of the guidance in Topic 606 should be applied, including the guidance on recognition, measurement, presentation and disclosure. ASU 2018-18 also adds a reference in ASC Topic 808, Collaborative Arrangements (Topic 808) to the unit of account guidance in Topic 606 and requires that it be applied only to assess whether transactions in a collaborative arrangement are in the scope of Topic 606. ASU 2018-18 will preclude entities from presenting amounts related to transactions with a counterparty in a collaborative arrangement that is not a customer as revenue from contracts with customers. ASU 2018-18 is effective for us for all interim and annual reporting periods beginning after December 15, 2019. Early adoption is permitted. We are in the process of assessing the impact of ASU 2018-18 on our Condensed Consolidated Financial Statements. In January 2017, the FASB issued ASU No. 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04) . ASU 2017-04 eliminated Step 2 from the goodwill impairment test. Instead, under the amendments in ASU 2017-04, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. Additionally, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. ASU 2017-04 is effective for all interim and annual reporting periods beginning after December 15, 2019. Early adoption is permitted. We do not expect the adoption of ASU 2017-04 to have a material impact on our Condensed Consolidated Financial Statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326) (ASU 2016-13) . ASU 2016-13 implements an impairment model, known as the current expected credit loss model that is based on expected losses rather than incurred losses. Under the new guidance, an entity will recognize as an allowance its estimate of expected credit losses. 2016-13 is effective for all interim and annual reporting periods beginning after December 15, 2019. Early adoption is permitted. We do not expect the adoption of ASU 2016-13 to have a material impact on our Condensed Consolidated Financial Statements.
Revenues	Chargebacks and discounts for prompt payment are recorded as a reduction of trade receivables and the remaining reserve balances are classified as Other current liabilities in the accompanying Condensed Consolidated Balance Sheets. Contract Assets and Liabilities We receive payments from our licensees based on billing schedules established in each contract. Amounts are recorded as accounts receivable when our right to consideration is unconditional. We may also recognize revenue in advance of the contractual billing schedule and such amounts are recorded as unbilled collaboration revenue when recognized. Unbilled collaboration revenue was zero as of both September 30, 2019 and December 31, 2018 Net product revenues are attributed to geographic region based on the ship-to location. Collaboration revenues are attributed to geographic region based on the location of our collaboration partners’ headquarters. Net product revenues, License revenues and Research and development services revenues were recorded in accordance with Topic 606 for all periods presented. Net product revenues and License revenues related to goods and intellectual property licenses transferred at a point in time and Research and development services revenues related to services performed over time. Other collaboration revenues, which included the p rofit on the U.S. commercialization of COTELLIC and net losses on product supply services, were recorded in accordance with Topic 808 for all periods presented .

Revenues (Tables)

Revenues (Tables)	9 Months Ended
	Sep. 27, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	Revenues by disaggregated category were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Product revenues: Gross product revenues $ 239,916 $ 193,356 $ 704,084 $ 525,438 Discounts and allowances (48,148 ) (30,410 ) (139,060 ) (82,384 ) Net product revenues 191,768 162,946 565,024 443,054 Collaboration revenues: License revenues (1) 68,035 51,323 128,937 152,261 Research and development services revenues (2) 12,988 10,560 35,814 27,464 Other collaboration revenues (3) (1,088 ) 568 (2,310 ) 2,445 Total collaboration revenues 79,935 62,451 162,441 182,170 Total revenues $ 271,703 $ 225,397 $ 727,465 $ 625,224 ____________________ (1) License revenues included the recognition of the portion of milestones allocated to the transfer of intellectual property licenses for which it had become probable in the current period that the milestone would be achieved and a significant revenue reversal would not occur, as well as royalty revenues from Ipsen Pharma SAS (Ipsen), Genentech and Daiichi Sankyo. (2) Research and development services revenues included the recognition of deferred revenue for the portion of upfront and milestone payments that have been allocated to research and development services performance obligations, as well as development cost reimbursements earned on our collaboration agreements. (3) Other collaboration revenues included the profit on the U.S. commercialization of COTELLIC from Genentech and revenues on product supply services provided to Ipsen and Takeda Pharmaceutical Company Ltd. (Takeda), which were offset by the 3% royalty we are required to pay GlaxoSmithKline (GSK) on the net sales by Ipsen of any product incorporating cabozantinib. Net product revenues, License revenues and Research and development services revenues were recorded in accordance with Topic 606 for all periods presented. Net product revenues and License revenues related to goods and intellectual property licenses transferred at a point in time and Research and development services revenues related to services performed over time. Other collaboration revenues, which included the p rofit on the U.S. commercialization of COTELLIC and net losses on product supply services, were recorded in accordance with Topic 808 for all periods presented . Net product revenues disaggregated by product were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 CABOMETYX $ 187,410 $ 158,262 $ 552,315 $ 428,317 COMETRIQ 4,358 4,684 12,709 14,737 Net product revenues $ 191,768 $ 162,946 $ 565,024 $ 443,054 Total revenues disaggregated by significant customer were as follows (dollars in thousands): Three Months Ended September 30, 2019 2018 Dollars Percent of Total Dollars Percent of Total Ipsen $ 76,016 28 % $ 57,186 25 % Caremark L.L.C. 35,703 13 % 30,707 14 % Affiliates of McKesson Corporation 31,901 12 % 26,597 12 % Affiliates of AmerisourceBergen Corporation 25,235 9 % 17,232 8 % Others, individually less than 10% of Total revenues for all periods presented 102,848 38 % 93,675 41 % Total revenues $ 271,703 100 % $ 225,397 100 % Nine Months Ended September 30, 2019 2018 Dollars Percent of Total Dollars Percent of Total Ipsen $ 120,133 17 % $ 145,038 23 % Caremark L.L.C. 105,638 15 % 83,516 13 % Affiliates of McKesson Corporation 88,496 12 % 71,249 11 % Affiliates of AmerisourceBergen Corporation 70,503 10 % 49,995 8 % Others, individually less than 10% of Total revenues for all periods presented 342,695 46 % 275,426 45 % Total revenues $ 727,465 100 % $ 625,224 100 % Total revenues disaggregated by geographic region were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 U.S. $ 194,484 $ 166,270 $ 572,957 $ 453,342 Europe 76,017 57,186 120,134 145,038 Japan 1,202 1,941 34,374 26,844 Total revenues $ 271,703 $ 225,397 $ 727,465 $ 625,224
Activities and Ending Reserve Balances for Significant Categories of Discounts and Allowances	The activities and ending reserve balances for each significant category of discounts and allowances (which constitute variable consideration) were as follows (in thousands): Chargebacks and Discounts for Prompt Payment Other Customer Credits/Fees and Co-pay Assistance Rebates Total Balance at December 31, 2018 $ 2,322 $ 3,038 $ 11,916 $ 17,276 Provision related to sales made in: Current period 92,769 11,190 35,422 139,381 Prior periods (130 ) (106 ) (85 ) (321 ) Payments and customer credits issued (92,317 ) (11,466 ) (33,127 ) (136,910 ) Balance at September 30, 2019 $ 2,644 $ 2,656 $ 14,126 $ 19,426

Collaboration Agreements (Table

Collaboration Agreements (Tables)	9 Months Ended
	Sep. 27, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Collaborative Revenues Under Collaboration Agreement	Collaboration revenues under the collaboration agreement with Takeda were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Takeda collaboration revenues $ 1,187 $ 1,940 $ 14,245 $ 6,843 Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Ipsen collaboration revenues $ 76,016 $ 57,186 $ 120,133 $ 145,038 Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Profits on U.S. commercialization $ 1,102 $ 1,935 $ 3,507 $ 6,004 Royalty revenues on ex-U.S. sales $ 1,614 $ 1,390 $ 4,426 $ 4,285 Collaboration revenues under the collaboration agreement with Daiichi Sankyo were as follows (in thousands): Nine Months Ended September 30, 2019 2018 Daiichi Sankyo collaboration revenues $ 20,130 $ 20,000 Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Royalties accruing to GSK $ 7,964 $ 6,268 $ 23,079 $ 17,021

Cash and Investments (Tables)

Cash and Investments (Tables)	9 Months Ended
	Sep. 27, 2019
Investments, Debt and Equity Securities [Abstract]
Reconciliation of Cash, Cash Equivalents, and Restricted Cash	A reconciliation of Cash, cash equivalents, and restricted cash reported within our Condensed Consolidated Balance Sheets to the amount reported within the accompanying Condensed Consolidated Statements of Cash Flows was as follows (in thousands): September 30, 2019 December 31, 2018 September 30, 2018 December 31, 2017 Cash and cash equivalents $ 242,317 $ 314,775 $ 353,623 $ 183,164 Restricted cash included in short-term restricted cash and investments — — 504 504 Restricted cash included in long-term restricted cash and investments 1,000 1,100 1,100 4,646 Cash, cash equivalents, and restricted cash as reported within the accompanying Condensed Consolidated Statements of Cash Flows $ 243,317 $ 315,875 $ 355,227 $ 188,314
Reconciliation of Cash, Cash Equivalents, and Restricted Cash	A reconciliation of Cash, cash equivalents, and restricted cash reported within our Condensed Consolidated Balance Sheets to the amount reported within the accompanying Condensed Consolidated Statements of Cash Flows was as follows (in thousands): September 30, 2019 December 31, 2018 September 30, 2018 December 31, 2017 Cash and cash equivalents $ 242,317 $ 314,775 $ 353,623 $ 183,164 Restricted cash included in short-term restricted cash and investments — — 504 504 Restricted cash included in long-term restricted cash and investments 1,000 1,100 1,100 4,646 Cash, cash equivalents, and restricted cash as reported within the accompanying Condensed Consolidated Statements of Cash Flows $ 243,317 $ 315,875 $ 355,227 $ 188,314
Investments by Security Type	Cash and investments by security type were as follows (in thousands): September 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Investments available-for-sale: Money market funds $ 26,641 $ — $ — $ 26,641 Commercial paper 332,239 — — 332,239 Corporate bonds 703,325 3,549 (67 ) 706,807 U.S. Treasury and government sponsored enterprises 152,531 143 (24 ) 152,650 Total investments available-for-sale 1,214,736 3,692 (91 ) 1,218,337 Cash and restricted cash 901 — — 901 Certificates of deposit 29,189 3 — 29,192 Total cash and investments $ 1,244,826 $ 3,695 $ (91 ) $ 1,248,430 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Investments available-for-sale: Money market funds $ 47,744 $ — $ — $ 47,744 Commercial paper 381,134 — (1 ) 381,133 Corporate bonds 344,741 180 (857 ) 344,064 U.S. Treasury and government sponsored enterprises 55,224 2 (25 ) 55,201 Total investments available-for-sale 828,843 182 (883 ) 828,142 Cash and restricted cash 6,883 — — 6,883 Certificates of deposit 16,596 — — 16,596 Total cash and investments $ 852,322 $ 182 $ (883 ) $ 851,621
Fair Value and Gross Unrealized Losses of Investments Available-for-Sale in an Unrealized Loss Position	The fair value and gross unrealized losses on investments available-for-sale in an unrealized loss position were as follows (in thousands): September 30, 2019 In an Unrealized Loss Position Less than 12 Months In an Unrealized Loss Position 12 Months or Greater Total Fair Value Gross Fair Value Gross Fair Value Gross Corporate bonds $ 73,064 $ (66 ) $ 4,398 $ (1 ) $ 77,462 $ (67 ) U.S. Treasury and government sponsored enterprises 46,744 (24 ) — — 46,744 (24 ) Total $ 119,808 $ (90 ) $ 4,398 $ (1 ) $ 124,206 $ (91 ) December 31, 2018 In an Unrealized Loss Position Less than 12 Months In an Unrealized Loss Position 12 Months or Greater Total Fair Value Gross Fair Value Gross Fair Value Gross Corporate bonds $ 236,162 $ (606 ) $ 39,627 $ (251 ) $ 275,789 $ (857 ) U.S. Treasury and government sponsored enterprises 28,105 (16 ) 9,182 (9 ) 37,287 (25 ) Commercial paper 7,091 (1 ) — — 7,091 (1 ) Total $ 271,358 $ (623 ) $ 48,809 $ (260 ) $ 320,167 $ (883 )
Fair Value of Cash Equivalents and Investments by Contractual Maturity	The fair value of investments available-for-sale by contractual maturity were as follows (in thousands): September 30, December 31, 2018 Maturing in one year or less $ 743,768 $ 674,455 Maturing after one year through five years 474,569 153,687 Total investments available-for-sale $ 1,218,337 $ 828,142

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 27, 2019
Inventory Disclosure [Abstract]
Inventory	Inventory consisted of the following (in thousands): September 30, December 31, 2018 Raw materials $ 1,906 $ 1,922 Work in process 11,035 6,170 Finished goods 7,311 3,836 Total $ 20,252 $ 11,928 Balance Sheet classification: Current portion included in Inventory $ 13,366 $ 9,838 Long-term portion included in Other long-term assets 6,886 2,090 Total $ 20,252 $ 11,928

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 27, 2019
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and equipment consisted of the following (in thousands): September 30, December 31, Leasehold improvements $ 33,769 $ 33,941 Computer equipment and software 17,017 15,022 Furniture and fixtures 13,053 12,709 Laboratory equipment 8,408 5,668 Construction in progress 617 866 72,864 68,206 Less: accumulated depreciation and amortization (23,397 ) (17,309 ) Property and equipment, net $ 49,467 $ 50,897

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 27, 2019
Share-based Payment Arrangement [Abstract]
Allocated Employee Stock-Based Compensation Expense	We allocated the stock-based compensation expense for our equity incentive plans and our 2000 Employee Stock Purchase Plan (ESPP) as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Research and development $ 4,301 $ 3,169 $ 13,745 $ 9,102 Selling, general and administrative 8,838 6,573 27,002 19,228 Total stock-based compensation $ 13,139 $ 9,742 $ 40,747 $ 28,330
Weighted Average Grant-Date Fair Value of Stock Options and ESPP Purchases	The weighted average grant-date fair value per share of stock options and ESPP purchases were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Stock options $ 7.71 $ 8.67 $ 8.57 $ 9.13 ESPP $ 5.39 $ 6.19 $ 4.93 $ 6.96
Valuation Assumptions Used to Estimate Grant-Date Fair Value	The grant-date fair value of stock option grants and ESPP purchases was estimated using the following assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Stock options: Risk-free interest rate 1.57 % 2.91 % 1.82 % 2.83 % Dividend yield — % — % — % — % Volatility 48 % 55 % 48 % 55 % Expected life 4.0 years 4.4 years 4.4 years 4.4 years ESPP: Risk-free interest rate 2.09 % 2.11 % 2.34 % 1.74 % Dividend yield — % — % — % — % Volatility 43 % 51 % 52 % 52 % Expected life 6 months 6 months 6 months 6 months
Stock Option Activity	Activity for stock options during the nine months ended September 30, 2019 was as follows (dollars in thousands , except per share amounts): Shares Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term Aggregate Intrinsic Value Options outstanding at December 31, 2018 22,674,062 $ 8.71 Granted 1,042,286 $ 20.81 Exercised (3,042,201 ) $ 4.94 Forfeited (160,241 ) $ 16.76 Expired (35,045 ) $ 23.41 Options outstanding at September 30, 2019 20,478,861 $ 9.80 3.4 years $ 186,407 Exercisable at September 30, 2019 15,860,131 $ 7.02 2.8 years $ 181,542
RSU Activity	Activity for RSUs during the nine months ended September 30, 2019 was as follows (dollars in thousands , except per share amounts): Shares Weighted Average Grant Date Fair Value Per Share Weighted Average Remaining Contractual Term Aggregate Intrinsic Value RSUs outstanding at December 31, 2018 4,857,334 $ 18.42 Awarded 5,635,362 $ 19.54 Vested and released (484,731 ) $ 12.33 Forfeited (258,142 ) $ 18.47 RSUs outstanding at September 30, 2019 9,749,823 $ 19.37 2.2 years $ 175,448

Net Income Per Share (Tables)

Net Income Per Share (Tables)	9 Months Ended
	Sep. 27, 2019
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Income Per Share	The basic and diluted net income per share were computed as follows (in thousands, except per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Numerator: Net income $ 97,452 $ 126,630 $ 252,269 $ 329,981 Denominator: Weighted-average shares of common stock outstanding used in computing basic net income per share 303,268 298,416 301,999 297,700 Dilutive securities 12,185 13,930 13,047 15,500 Weighted-average shares of common stock outstanding and dilutive securities used in computing diluted net income per share 315,453 312,346 315,046 313,200 Net income per share, basic $ 0.32 $ 0.42 $ 0.84 $ 1.11 Net income per share, diluted $ 0.31 $ 0.41 $ 0.80 $ 1.05
Potential Shares of Common Stock Not Included in the Computation of Diluted Net Income (Loss) Per Share	Potential shares of common stock not included in the computation of diluted net income per share because to do so would be anti-dilutive, were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Potentially dilutive securities 6,153 5,687 5,740 2,938

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 27, 2019
Fair Value Disclosures [Abstract]
Classification of Financial Assets Measured and Recorded at Fair Value on a Recurring Basis	The classifications within the fair value hierarchy of our financial assets that were measured and recorded at fair value on a recurring basis were as follows (in thousands): September 30, 2019 Level 1 Level 2 Total Money market funds $ 26,641 $ — $ 26,641 Commercial paper — 332,239 332,239 Corporate bonds — 706,807 706,807 U.S. Treasury and government sponsored enterprises — 152,650 152,650 Total investments available-for-sale 26,641 1,191,696 1,218,337 Certificates of deposit — 29,192 29,192 Total financial assets carried at fair value $ 26,641 $ 1,220,888 $ 1,247,529 December 31, 2018 Level 1 Level 2 Total Money market funds $ 47,744 $ — $ 47,744 Commercial paper — 381,133 381,133 Corporate bonds — 344,064 344,064 U.S. Treasury and government sponsored enterprises — 55,201 55,201 Total investments available-for-sale 47,744 780,398 828,142 Certificates of deposit — 16,596 16,596 Total financial assets carried at fair value $ 47,744 $ 796,994 $ 844,738

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 27, 2019
Leases [Abstract]
Balance Sheet Classification of Lease Liabilities	The balance sheet classification of our lease liabilities were as follows (in thousands): September 30, December 31, 2018 Operating lease liabilities: Current portion included in Other current liabilities $ 2,695 $ 2,738 Long-term portion of lease liabilities 23,661 12,099 Total operating lease liabilities 26,356 14,837 Financing lease liabilities: Current portion included in Other current liabilities 50 49 Long-term portion of lease liabilities 44 79 Total financing lease liabilities 94 128 Total lease liabilities $ 26,450 $ 14,965
Components of Lease Expense	The components of lease costs for operating leases, which were included in Selling, general and administrative expenses in our Condensed Consolidated Statements of Income, were as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Operating lease cost $ 692 $ 1,614 $ 1,768 $ 3,587 Variable lease cost 274 363 654 1,366 Total lease costs $ 966 $ 1,977 $ 2,422 $ 4,953
Maturities of Operating Lease Liabilities	As of September 30, 2019 , the maturities of our operating lease liabilities were as follows (in thousands): Remainder of 2019 $ 745 Years ending December 31, 2020 3,625 2021 3,731 2022 3,852 2023 3,959 Thereafter 17,444 Total lease payments 33,356 Less: Present value adjustment (5,258 ) Tenant improvement reimbursements (1) (1,742 ) Operating lease liabilities $ 26,356 ____________________ (1) Represents anticipated tenant improvement reimbursements applicable to the portion of the 1601 Expansion Space.

Organization and Summary of S_3

Organization and Summary of Significant Accounting Policies (Details)	9 Months Ended
	Sep. 27, 2019segmentproduct
Organization And Summary Of Significant Policies [Line Items]
Number of products that entered in the commercial marketplace	4
Number of business segments | segment	1
Products Derived from Cabozantinib
Organization And Summary Of Significant Policies [Line Items]
Number of products that entered in the commercial marketplace	2
Resulting from Discovery Efforts
Organization And Summary Of Significant Policies [Line Items]
Number of products that entered in the commercial marketplace	2

Revenues - Revenues by Disaggre

Revenues - Revenues by Disaggregated Category (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 271,703	$ 225,397	$ 727,465	$ 625,224
Collaborative Arrangement with Ipsen
Disaggregation of Revenue [Line Items]
Total revenues	76,016	57,186	$ 120,133	145,038
GSK | Collaborative Arrangement with Ipsen
Disaggregation of Revenue [Line Items]
Percent of royalty on net sale			3.00%
Net product revenues
Disaggregation of Revenue [Line Items]
Total revenues	191,768	162,946	$ 565,024	443,054
Gross product revenues
Disaggregation of Revenue [Line Items]
Total revenues	239,916	193,356	704,084	525,438
Discounts and allowances
Disaggregation of Revenue [Line Items]
Total revenues	48,148	30,410	139,060	82,384
Total collaboration revenues
Disaggregation of Revenue [Line Items]
Total revenues	79,935	62,451	162,441	182,170
License revenues
Disaggregation of Revenue [Line Items]
Total revenues	68,035	51,323	128,937	152,261
Research and development services revenues
Disaggregation of Revenue [Line Items]
Total revenues	12,988	10,560	35,814	27,464
Other collaboration revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ (1,088)	$ 568	$ (2,310)	$ 2,445

Revenues - Net Product Revenues

Revenues - Net Product Revenues Disaggregated by Product (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Disaggregation of Revenue [Line Items]
Net product revenues	$ 271,703	$ 225,397	$ 727,465	$ 625,224
Net product revenues
Disaggregation of Revenue [Line Items]
Net product revenues	191,768	162,946	565,024	443,054
CABOMETYX
Disaggregation of Revenue [Line Items]
Net product revenues	187,410	158,262	552,315	428,317
COMETRIQ
Disaggregation of Revenue [Line Items]
Net product revenues	$ 4,358	$ 4,684	$ 12,709	$ 14,737

Revenues - Revenues Disaggregat

Revenues - Revenues Disaggregated by Significant Customer (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 271,703	$ 225,397	$ 727,465	$ 625,224
Revenue | Customer Concentration Risk
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Percent of total revenues	100.00%	100.00%	100.00%	100.00%
Ipsen
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 76,016	$ 57,186	$ 120,133	$ 145,038
Ipsen | Revenue | Customer Concentration Risk
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Percent of total revenues	28.00%	25.00%	17.00%	23.00%
Caremark L.L.C.
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 35,703	$ 30,707	$ 105,638	$ 83,516
Caremark L.L.C. | Revenue | Customer Concentration Risk
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Percent of total revenues	13.00%	14.00%	15.00%	13.00%
Affiliates of McKesson Corporation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 31,901	$ 26,597	$ 88,496	$ 71,249
Affiliates of McKesson Corporation | Revenue | Customer Concentration Risk
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Percent of total revenues	12.00%	12.00%	12.00%	11.00%
Affiliates of AmerisourceBergen Corporation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 25,235	$ 17,232	$ 70,503	$ 49,995
Affiliates of AmerisourceBergen Corporation | Revenue | Customer Concentration Risk
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Percent of total revenues	9.00%	8.00%	10.00%	8.00%
Others, individually less than 10% of Total revenues for all periods presented
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total revenues	$ 102,848	$ 93,675	$ 342,695	$ 275,426
Others, individually less than 10% of Total revenues for all periods presented | Revenue | Customer Concentration Risk
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Percent of total revenues	38.00%	41.00%	46.00%	45.00%

Revenues - Revenues Disaggreg_2

Revenues - Revenues Disaggregated by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 271,703	$ 225,397	$ 727,465	$ 625,224
U.S.
Disaggregation of Revenue [Line Items]
Total revenues	194,484	166,270	572,957	453,342
Europe
Disaggregation of Revenue [Line Items]
Total revenues	76,017	57,186	120,134	145,038
Japan
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,202	$ 1,941	$ 34,374	$ 26,844

Revenues - Activities and Endin

Revenues - Activities and Ending Reserve Balances for Significant Categories of Discounts and Allowances (Details) $ in Thousands	9 Months Ended
	Sep. 27, 2019USD ($)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at December 31, 2018	$ 17,276
Provision related to sales made in:
Current period	139,381
Prior periods	(321)
Payments and customer credits issued	(136,910)
Balance at September 30, 2019	19,426
Chargebacks and Discounts for Prompt Payment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at December 31, 2018	2,322
Provision related to sales made in:
Current period	92,769
Prior periods	(130)
Payments and customer credits issued	(92,317)
Balance at September 30, 2019	2,644
Other Customer Credits/Fees and Co-pay Assistance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at December 31, 2018	3,038
Provision related to sales made in:
Current period	11,190
Prior periods	(106)
Payments and customer credits issued	(11,466)
Balance at September 30, 2019	2,656
Rebates
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at December 31, 2018	11,916
Provision related to sales made in:
Current period	35,422
Prior periods	(85)
Payments and customer credits issued	(33,127)
Balance at September 30, 2019	$ 14,126

Revenues - Contract Assets and

Revenues - Contract Assets and Liabilities under Topic 606 (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018	Dec. 28, 2018
Revenue from Contract with Customer [Abstract]
Unbilled collaboration revenue	$ 0		$ 0		$ 0
Deferred revenue	15,399		15,399		$ 15,897	[1]
Amount of revenues recognized included in the beginning contract liability balance			2,700	$ 6,100
Revenues recognized for performance obligations satisfied in previous periods	$ 67,700	$ 48,200	$ 129,000	$ 151,800
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Collaboration Agreements - Coll

Collaboration Agreements - Collaboration Revenues under the Collaboration Agreement with Ipsen (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 271,703	$ 225,397	$ 727,465	$ 625,224
Collaborative Arrangement with Ipsen
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 76,016	$ 57,186	$ 120,133	$ 145,038

Collaboration Agreements - Ipse

Collaboration Agreements - Ipsen Collaboration (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018	[1]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Net contract liability	$ 15,399	$ 15,897
Collaborative Arrangement with Ipsen
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Remaining performance obligation	47,100
Net contract liability	$ 7,200
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Collaboration Agreements - Co_2

Collaboration Agreements - Collaboration Revenues under the Collaboration Agreement with Takeda (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 271,703	$ 225,397	$ 727,465	$ 625,224
Collaborative Arrangement with Takeda
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 1,187	$ 1,940	$ 14,245	$ 6,843

Collaboration Agreements - Take

Collaboration Agreements - Takeda Collaboration (Details) - Collaborative Arrangement with Takeda - USD ($) $ in Millions	Apr. 29, 2019	Apr. 28, 2019	Sep. 27, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Limit on reimbursement per year	$ 1
Increase in maximum amount eligible for development and regulatory milestones	12
Maximum amount eligible for development and regulatory milestones	102
Milestone payments earned	16	$ 10
Increase in maximum amount eligible for commercial milestones under collaborations agreement	6
Maximum amount eligible for commercial milestones under collaborations agreement	$ 89
Remaining performance obligation			$ 18.7
Net contract liability			$ 8.2

Collaboration Agreements - Roya

Collaboration Agreements - Royalty Revenues under the Collaboration Agreement with Genentech (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalty revenues on ex-U.S. sales	$ 271,703	$ 225,397	$ 727,465	$ 625,224
Collaborative Arrangement with Genentech
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Profits and losses on U.S. commercialization	1,102	1,935	3,507	6,004
Royalty revenues on ex-U.S. sales	$ 1,614	$ 1,390	$ 4,426	$ 4,285

Collaboration Agreements - Daii

Collaboration Agreements - Daiichi Sankyo (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues		$ 271,703	$ 225,397	$ 727,465	$ 625,224
Collaboration revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues		79,935	62,451	162,441	182,170
Collaboration Agreement with Daiichi Sankyo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues		$ 0	$ 0	$ 20,130	$ 20,000
Percent of royalty on net sale				0.50%
Collaboration Agreement with Daiichi Sankyo | Collaboration revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 20,000

Collaboration Agreements - Co_3

Collaboration Agreements - Collaboration Revenues under the Collaboration Agreement with Daiichi Sankyo (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 271,703	$ 225,397	$ 727,465	$ 625,224
Collaboration Agreement with Daiichi Sankyo
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total revenues	$ 0	$ 0	$ 20,130	$ 20,000

Collaboration Agreements - Icon

Collaboration Agreements - Iconic Therapeutics, Inc. (Iconic) Collaboration (Details) - Collaboration Agreement with Iconic Therapeutics, Inc. - USD ($) $ in Millions	1 Months Ended
	May 31, 2019	Sep. 27, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment	$ 7.5
Preclinical development funding commitment accrued		$ 6.6
Option exercise fee payment, if exercised		20
Maximum amount eligible for development, regulatory and first-sale milestones		190.6
Maximum amount eligible for commercial milestones under collaborations agreement		$ 262.5

Collaboration Agreements - Auri

Collaboration Agreements - Aurigene Discovery Technologies Limited (Aurigene) Collaboration (Details) $ in Millions	1 Months Ended
	Jul. 31, 2019USD ($)program	Sep. 27, 2019USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Additional option payments	$ 7.5
Collaboration Agreement With Aurigene Discovery Technologies Limited Collaboration Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration agreement, number of programs | program	6
Upfront payment	$ 10
Collaboration agreement, number of preexisting programs | program	3
Collaboration agreement, number of drug discovery programs | program	3
Research and development obligation	$ 32.6
Preclinical development funding commitment accrued		$ 1.3
Maximum amount eligible for development and regulatory milestones	148.8
Maximum amount eligible for commercial milestones under collaborations agreement	280
Collaboration Agreement With Aurigene Discovery Technologies Limited Collaboration Agreement | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Option exercise fee payment, if exercised	10
Collaboration Agreement With Aurigene Discovery Technologies Limited Collaboration Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Option exercise fee payment, if exercised	$ 12

Collaboration Agreements - Ro_2

Collaboration Agreements - Royalty Revenues under the Collaboration Agreement with GSK (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Collaboration Agreement with GlaxoSmithKline
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Royalties accruing to GSK	$ 7,964	$ 6,268	$ 23,079	$ 17,021
GSK | Collaborative Arrangement with Ipsen
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percent of royalty on net sale			3.00%

Cash and Investments - Reconcil

Cash and Investments - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018		Sep. 28, 2018	Dec. 29, 2017
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 242,317	$ 314,775	[1]	$ 353,623	$ 183,164
Restricted cash included in short-term restricted cash and investments	0	0	[1]	504	504
Restricted cash included in long-term restricted cash and investments	1,000	1,100	[1]	1,100	4,646
Cash, cash equivalents, and restricted cash as reported within the accompanying Condensed Consolidated Statements of Cash Flows	$ 243,317	$ 315,875		$ 355,227	$ 188,314
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Cash and Investments - Investme

Cash and Investments - Investments by Security Type (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018	Sep. 28, 2018	Dec. 29, 2017
Investment [Line Items]
Investments, available-for-sale, Amortized Cost	$ 1,214,736	$ 828,843
Investments available-for-sale, Gross Unrealized Gains	3,692	182
Investments available-for-sale, Gross Unrealized Losses	(91)	(883)
Investments available-for-sale, Fair Value	1,218,337	828,142
Cash, cash equivalents, and restricted cash as reported within the accompanying Condensed Consolidated Statements of Cash Flows	243,317	315,875	$ 355,227	$ 188,314
Total cash and investments, Amortized Cost	1,244,826	852,322
Total cash and investments, Gross Unrealized Gains	3,695	182
Total cash and investments, Gross Unrealized Losses	(91)	(883)
Total cash and investments, Fair Value	1,248,430	851,621
Money market funds
Investment [Line Items]
Investments, available-for-sale, Amortized Cost	26,641	47,744
Investments available-for-sale, Gross Unrealized Gains	0	0
Investments available-for-sale, Gross Unrealized Losses	0	0
Investments available-for-sale, Fair Value	26,641	47,744
Commercial paper
Investment [Line Items]
Investments, available-for-sale, Amortized Cost	332,239	381,134
Investments available-for-sale, Gross Unrealized Gains	0	0
Investments available-for-sale, Gross Unrealized Losses	0	(1)
Investments available-for-sale, Fair Value	332,239	381,133
Corporate bonds
Investment [Line Items]
Investments, available-for-sale, Amortized Cost	703,325	344,741
Investments available-for-sale, Gross Unrealized Gains	3,549	180
Investments available-for-sale, Gross Unrealized Losses	(67)	(857)
Investments available-for-sale, Fair Value	706,807	344,064
U.S. Treasury and government sponsored enterprises
Investment [Line Items]
Investments, available-for-sale, Amortized Cost	152,531	55,224
Investments available-for-sale, Gross Unrealized Gains	143	2
Investments available-for-sale, Gross Unrealized Losses	(24)	(25)
Investments available-for-sale, Fair Value	152,650	55,201
Cash and restricted cash
Investment [Line Items]
Investments available-for-sale, Gross Unrealized Gains		0
Investments available-for-sale, Gross Unrealized Losses		0
Cash, cash equivalents, and restricted cash as reported within the accompanying Condensed Consolidated Statements of Cash Flows	901	6,883
Cash, cash equivalents, and restricted cash, Gross Unrealized Gains	0
Cash, cash equivalents, and restricted cash, Gross Unrealized Losses	0
Cash, restricted cash and certificates of deposit, Fair Value	901	6,883
Certificates of deposit
Investment [Line Items]
Investments available-for-sale, Gross Unrealized Gains		0
Investments available-for-sale, Gross Unrealized Losses		0
Cash, cash equivalents, and restricted cash as reported within the accompanying Condensed Consolidated Statements of Cash Flows	29,189	16,596
Cash, cash equivalents, and restricted cash, Gross Unrealized Gains	3
Cash, cash equivalents, and restricted cash, Gross Unrealized Losses	0
Cash, restricted cash and certificates of deposit, Fair Value	$ 29,192	$ 16,596

Cash and Investments - Fair Val

Cash and Investments - Fair Value and Gross Unrealized Losses of Investments Available-for-Sale in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
In an Unrealized Loss Position Less than 12 Months, Fair Value	$ 119,808	$ 271,358
In an Unrealized Loss Position Less than 12 Months, Gross Unrealized Losses	(90)	(623)
In an Unrealized Loss Position 12 Months or Greater, Fair Value	4,398	48,809
In an Unrealized Loss Position 12 Months or Greater, Gross Unrealized Losses	(1)	(260)
Total, Fair Value	124,206	320,167
Total, Gross Unrealized Losses	(91)	(883)
Corporate bonds
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
In an Unrealized Loss Position Less than 12 Months, Fair Value	73,064	236,162
In an Unrealized Loss Position Less than 12 Months, Gross Unrealized Losses	(66)	(606)
In an Unrealized Loss Position 12 Months or Greater, Fair Value	4,398	39,627
In an Unrealized Loss Position 12 Months or Greater, Gross Unrealized Losses	(1)	(251)
Total, Fair Value	77,462	275,789
Total, Gross Unrealized Losses	(67)	(857)
U.S. Treasury and government sponsored enterprises
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
In an Unrealized Loss Position Less than 12 Months, Fair Value	46,744	28,105
In an Unrealized Loss Position Less than 12 Months, Gross Unrealized Losses	(24)	(16)
In an Unrealized Loss Position 12 Months or Greater, Fair Value	0	9,182
In an Unrealized Loss Position 12 Months or Greater, Gross Unrealized Losses	0	(9)
Total, Fair Value	46,744	37,287
Total, Gross Unrealized Losses	$ (24)	(25)
Commercial paper
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
In an Unrealized Loss Position Less than 12 Months, Fair Value		7,091
In an Unrealized Loss Position Less than 12 Months, Gross Unrealized Losses		(1)
In an Unrealized Loss Position 12 Months or Greater, Fair Value		0
In an Unrealized Loss Position 12 Months or Greater, Gross Unrealized Losses		0
Total, Fair Value		7,091
Total, Gross Unrealized Losses		$ (1)

Cash and Investments - Narrativ

Cash and Investments - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 27, 2019USD ($)investment	Sep. 28, 2018USD ($)	Sep. 27, 2019USD ($)investment	Sep. 28, 2018USD ($)	Dec. 28, 2018USD ($)investment
Investments, Debt and Equity Securities [Abstract]
Gain (loss) on sales of investments available-for-sale	$ 0	$ 0	$ 0	$ 0
Number of investments in an unrealized loss position | investment	43		43		199
Other-than-temporary impairment charges on available-for-sale securities	$ 0	$ 0	$ 0
Beneficial ownership interest by BlackRock (more than)					10.00%
Fair value of cash and investments managed by BlackRock	470,800,000		470,800,000		$ 298,500,000
Fair value of cash and investments managed by BlackRock in the BlackRock Liquidity Money Market Fund	1,900,000		1,900,000		$ 3,000,000
Payable to BlackRock	$ 9,000,000		9,000,000
Fees for advisory services paid to BlackRock			$ 200,000

Cash and Investments - Fair V_2

Cash and Investments - Fair Value of Cash Equivalents and Investments by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018
Investments, Debt and Equity Securities [Abstract]
Maturing in one year or less	$ 743,768	$ 674,455
Maturing after one year through five years	474,569	153,687
Total investments available-for-sale	$ 1,218,337	$ 828,142

Inventory (Details)

Inventory (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Dec. 28, 2018
Inventory [Line Items]
Raw materials	$ 1,906		$ 1,922
Work in process	11,035		6,170
Finished goods	7,311		3,836
Total	20,252		11,928
Write-downs on inventory	400	$ 800
Current portion included in Inventory
Inventory [Line Items]
Total	13,366		9,838
Long-term portion included in Other long-term assets
Inventory [Line Items]
Total	$ 6,886		$ 2,090

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 72,864	$ 68,206
Less: accumulated depreciation and amortization	(23,397)	(17,309)
Property and equipment, net	49,467	50,897	[1]
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	33,769	33,941
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	17,017	15,022
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	13,053	12,709
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	8,408	5,668
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 617	$ 866
[1]	The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.

Property and Equipment - Narrat

Property and Equipment - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 2.1	$ 1.7	$ 6.1	$ 2.9

Stock-Based Compensation - Allo

Stock-Based Compensation - Allocated Employee Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 13,139	$ 9,742	$ 40,747	$ 28,330
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	4,301	3,169	13,745	9,102
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation	$ 8,838	$ 6,573	$ 27,002	$ 19,228

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018	Dec. 28, 2018	Jun. 28, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)	6,024,995		6,024,995
Compensation expense	$ 13,139	$ 9,742	$ 40,747	$ 28,330
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	38,000		$ 38,000
Weighted-average cost recognition period			2 years 3 months 18 days
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 166,000		$ 166,000
Weighted-average cost recognition period			2 years 9 months 18 days
RSUs awarded (in shares)			5,635,362
Product revenue related performance targets, shares vested and released (in shares)	9,749,823		9,749,823		4,857,334
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs awarded (in shares)			1,926,605		693,131
Compensation expense	$ 900		$ 3,500
PSUs | Achieved
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Product revenue related performance targets, shares vested and released (in shares)						114,843
PSUs | Probable
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	1,700		1,700
Product revenue related performance targets, shares vested and released (in shares)						172,272
PSUs | Not Probable
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 82,400		$ 82,400
PSUs, achieved before December 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum potential to vest, percentage			150.00%
Maximum potential to vest (in shares)			963,136
PSUs, second product approval
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum potential to vest, percentage			200.00%
Maximum potential to vest (in shares)			1,926,605

Stock-Based Compensation - Weig

Stock-Based Compensation - Weighted Average Grant-Date Fair Value of Stock Options and ESPP Purchases (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value (in dollars per share)	$ 7.71	$ 8.67	$ 8.57	$ 9.13
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value (in dollars per share)	$ 5.39	$ 6.19	$ 4.93	$ 6.96

Stock-Based Compensation - Valu

Stock-Based Compensation - Valuation Assumptions Used to Estimate Grant-Date Fair Value (Details)	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.57%	2.91%	1.82%	2.83%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Expected volatility	48.00%	55.00%	48.00%	55.00%
Expected life	4 years	4 years 4 months 24 days	4 years 4 months 24 days	4 years 4 months 24 days
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.09%	2.11%	2.34%	1.74%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Expected volatility	43.00%	51.00%	52.00%	52.00%
Expected life	6 months	6 months	6 months	6 months

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 27, 2019USD ($)$ / sharesshares
Shares
Options outstanding at beginning of period (in shares) | shares	22,674,062
Granted (in shares) | shares	1,042,286
Exercised (in shares) | shares	(3,042,201)
Forfeited (in shares) | shares	(160,241)
Expired (in shares) | shares	(35,045)
Options outstanding at end of period (in shares) | shares	20,478,861
Exercisable at end of period (in shares) | shares	15,860,131
Weighted Average Exercise Price Per Share
Options outstanding at beginning of period (in dollars per share) | $ / shares	$ 8.71
Granted (in dollars per share) | $ / shares	20.81
Exercised (in dollars per share) | $ / shares	4.94
Forfeited (in dollars per share) | $ / shares	16.76
Expired (in dollars per share) | $ / shares	23.41
Options outstanding at end of period (in dollars per share) | $ / shares	9.80
Exercisable at end of period (in dollars per share) | $ / shares	$ 7.02
Weighted Average Remaining Contractual Term
Options outstanding at end of period	3 years 4 months 24 days
Exercisable at end of period	2 years 9 months 18 days
Aggregate Intrinsic Value
Options outstanding at end of period | $	$ 186,407
Exercisable at end of period | $	$ 181,542

Stock-Based Compensation - RSU

Stock-Based Compensation - RSU Activity (Details) - RSUs $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 27, 2019USD ($)$ / sharesshares
Shares
RSUs outstanding at beginning of period (in shares) | shares	4,857,334
Awarded (in shares) | shares	5,635,362
Vested and released (in shares) | shares	(484,731)
Forfeited (in shares) | shares	(258,142)
RSUs outstanding at end of period (in shares) | shares	9,749,823
Weighted Average Grant Date Fair Value Per Share
RSUs outstanding at beginning of period (in dollars per share) | $ / shares	$ 18.42
Awarded (in dollars per share) | $ / shares	19.54
Vested and released (in dollars per share) | $ / shares	12.33
Forfeited (in dollars per share) | $ / shares	18.47
RSUs outstanding at end of period (in dollars per share) | $ / shares	$ 19.37
Weighted Average Remaining Contractual Term
RSUs outstanding at end of period	2 years 2 months 12 days
Aggregate Intrinsic Value
RSUs outstanding at end of period | $	$ 175,448

Income Taxes (Details)

Income Taxes (Details)	3 Months Ended			9 Months Ended
	Sep. 27, 2019	Sep. 29, 2018	Sep. 28, 2018	Sep. 27, 2019	Sep. 29, 2018	Sep. 28, 2018
Income Tax Disclosure [Abstract]
Effective income tax rate	20.50%		1.80%	19.40%		1.70%
U.S. federal statutory rate	21.00%	21.00%		21.00%	21.00%

Net Income Per Share - Computat

Net Income Per Share - Computation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Numerator:
Net income	$ 97,452	$ 126,630	$ 252,269	$ 329,981
Denominator:
Weighted-average shares of common stock outstanding used in computing basic net income per share (in shares)	303,268	298,416	301,999	297,700
Dilutive securities (in shares)	12,185	13,930	13,047	15,500
Weighted-average shares of common stock outstanding and dilutive securities used in computing diluted net income per share (in shares)	315,453	312,346	315,046	313,200
Net income per share, basic (in dollars per share)	$ 0.32	$ 0.42	$ 0.84	$ 1.11
Net income per share, diluted (in dollars per share)	$ 0.31	$ 0.41	$ 0.80	$ 1.05

Net Income Per Share - Potentia

Net Income Per Share - Potential Shares of Common Stock Not Included in the Computation of Diluted Net Income (Loss) Per Share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Potentially dilutive securities
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	6,153	5,687	5,740	2,938

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	$ 1,218,337	$ 828,142
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	1,218,337	828,142
Total financial assets carried at fair value	1,247,529	844,738
Level 1 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	26,641	47,744
Total financial assets carried at fair value	26,641	47,744
Level 2 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	1,191,696	780,398
Total financial assets carried at fair value	1,220,888	796,994
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	26,641	47,744
Money market funds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	26,641	47,744
Money market funds | Level 1 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	26,641	47,744
Money market funds | Level 2 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	0	0
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	332,239	381,133
Commercial paper | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	332,239	381,133
Commercial paper | Level 1 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	0	0
Commercial paper | Level 2 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	332,239	381,133
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	706,807	344,064
Corporate bonds | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	706,807	344,064
Corporate bonds | Level 1 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	0	0
Corporate bonds | Level 2 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	706,807	344,064
U.S. Treasury and government sponsored enterprises
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	152,650	55,201
U.S. Treasury and government sponsored enterprises | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	152,650	55,201
U.S. Treasury and government sponsored enterprises | Level 1 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	0	0
U.S. Treasury and government sponsored enterprises | Level 2 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investments available-for-sale	152,650	55,201
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Certificates of deposit	29,192	16,596
Certificates of deposit | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Certificates of deposit	29,192	16,596
Certificates of deposit | Level 1 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Certificates of deposit	0	0
Certificates of deposit | Level 2 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Certificates of deposit	$ 29,192	$ 16,596

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Thousands	1 Months Ended	9 Months Ended
	May 31, 2017	Sep. 27, 2019USD ($)ft²renewal_option	Aug. 30, 2019ft²	Apr. 30, 2019USD ($)ft²	Jan. 31, 2019USD ($)
Lessee, Lease, Description [Line Items]
Tenant improvement allowance		$ 1,742
Cash paid for amounts included in the measurement of lease liabilities		$ 2,100
Weighted average operating discount rate used to determine the operating lease liability		4.20%
Weighted average remaining lease term for operating lease		8 years 3 months 18 days
Alameda, California
Lessee, Lease, Description [Line Items]
Area of lease property (in square feet) | ft²		169,606
Tenant improvement reimbursements					$ 8,200
Number of options to extend the Lease | renewal_option		2
Option to terminate lease (after period)	8 years
Lease option to extend period		5 years
Operating lease, expansion (in square feet) | ft²			59,335	37,544
Operating lease, surrendered (in square feet) | ft²				2,703
Tenant improvement allowance				$ 1,700

Leases - Balance Sheet Classifi

Leases - Balance Sheet Classification of Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018
Operating lease liabilities:
Current portion included in Other current liabilities	$ 2,695	$ 2,738
Long-term portion of lease liabilities	23,661	12,099
Total operating lease liabilities	26,356	14,837
Financing lease liabilities:
Current portion included in Other current liabilities	50	49
Long-term portion of lease liabilities	44	79
Financing obligation for build-to-suit lease	94	128
Total lease liabilities	$ 26,450	$ 14,965

Leases - Components of Lease Ex

Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2019	Sep. 28, 2018	Sep. 27, 2019	Sep. 28, 2018
Leases [Abstract]
Operating lease cost	$ 692	$ 1,614	$ 1,768	$ 3,587
Variable lease cost	274	363	654	1,366
Total lease costs	$ 966	$ 1,977	$ 2,422	$ 4,953

Leases - Maturities of Operatin

Leases - Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018
Maturities of Operating Lease Liabilities
Remainder of 2019	$ 745
Years ending December 31,
2020	3,625
2021	3,731
2022	3,852
2023	3,959
Thereafter	17,444
Total lease payments	33,356
Less:
Present value adjustment	(5,258)
Tenant improvement reimbursements	(1,742)
Operating lease liabilities	$ 26,356	$ 14,837

Subsequent Events (Details)

Subsequent Events (Details) $ in Thousands	Oct. 25, 2019USD ($)ft²renewal_option	May 31, 2017	Sep. 27, 2019ft²renewal_option	Aug. 30, 2019ft²	Apr. 30, 2019ft²
Alameda, California
Subsequent Event [Line Items]
Area of lease property (in square feet)			169,606
Number of options to extend the Lease | renewal_option			2
Lease option to extend period			5 years
Option to terminate lease (after period)		8 years
Operating lease, expansion (in square feet)				59,335	37,544
Subsequent Event | Built-To-Suit Lease
Subsequent Event [Line Items]
Option to terminate lease (after period)	180 months
Subsequent Event | Built-To-Suit Lease | Alameda, California
Subsequent Event [Line Items]
Area of lease property (in square feet)	220,000
Operating lease term	242 months
Estimated monthly base rent under Build-to-Suite Leases | $	$ 726
Monthly base rent, lease not yet commenced, annual percentage increase	3.00%
Number of options to extend the Lease | renewal_option	2
Lease option to extend period	5 years

Uncategorized Items - exel20190

Label	Element	Value
Accounting Standards Update 2014-09 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 258,505,000
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	258,505,000
Accounting Standards Update 2016-02 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	234,000
Accounting Standards Update 2016-02 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 234,000