Organization and Summary of Significant Accounting Policies	3 Months Ended
	Apr. 02, 2021
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. Our drug discovery and development capabilities and commercialization platform are the foundations upon which we intend to bring to market novel, effective and tolerable therapies to provide cancer patients with additional treatment options. Since we were founded in 1994, four products resulting from our discovery efforts have progressed through clinical development, received regulatory approval and established a commercial presence in various geographies around the world. Two are derived from cabozantinib, our flagship molecule, an inhibitor of multiple tyrosine kinases including MET, AXL, VEGF receptors and RET. Our cabozantinib products are: CABOMETYX® (cabozantinib) tablets approved for advanced renal cell carcinoma (RCC), both alone and in combination with Bristol Myers Squibb Company’s OPDIVO® (nivolumab), and for previously treated hepatocellular carcinoma (HCC); and COMETRIQ® (cabozantinib) capsules approved for progressive, metastatic medullary thyroid cancer. For these types of cancer, cabozantinib has become or is becoming a standard of care. Beyond these approved indications, cabozantinib is currently the focus of a broad clinical development program and is being investigated both alone and in combination with other therapies in a wide variety of cancers. The other two products resulting from our discovery efforts are: COTELLIC® (cobimetinib), an inhibitor of MEK, approved as part of multiple regimens to treat 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, approved for the treatment of hypertension in Japan and licensed to Daiichi Sankyo Company, Limited (Daiichi Sankyo). We remain committed to expanding our oncology product pipeline through our drug discovery efforts, which encompass both small molecule and biologics programs with multiple modalities and mechanisms of action. Basis of Presentation 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. 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. Operating results for the three months ended March 31, 2021 are not necessarily indicative of the results that may be expected for the year ending December 31, 2021 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, 2020, included in our Annual Report on Form 10-K submitted to the SEC on February 10, 2021. We have adopted a 52- or 53-week fiscal year policy that generally ends on the Friday closest to December 31st. Fiscal year 2021, which is a 52-week fiscal year, will end on December 31, 2021 and fiscal year 2020, which was a 52-week fiscal year, ended on January 1, 2021. For convenience, references in this report as of and for the three months ended April 2, 2021 and April 3, 2020, and as of and for the fiscal year ended January 1, 2021, are indicated as being as of and for the fiscal periods ended March 31, 2021 and March 31, 2020 and the year ended December 31, 2020, respectively. 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, we evaluate our significant estimates. 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. Reclassifications Certain prior period amounts in the accompanying Condensed Consolidated Financial Statements have been reclassified to conform to the current period presentation. Such reclassifications did not impact previously reported total revenues, income from operations, net income, total assets, total liabilities or total stockholders’ equity. Significant Accounting Policies Except for the foreign currency forward contracts for non-designated hedges, there have been no material changes to our significant accounting policies during the three months ended March 31, 2021, as compared to the significant accounting policies disclosed in Note 1 – Significant Accounting Policies included in the our Annual Report on Form 10-K for the year ended December 31, 2020. Foreign Currency Forward Contracts for Non-Designated Hedges We may use forward foreign currency exchange contracts (forward contracts) to hedge certain operational exposures resulting from potential changes in foreign currency exchange rates. Our strategy is to enter into foreign currency forward contracts so that increases or decreases in our foreign currency exposures are offset by gains or losses on the foreign currency forward contracts thereby mitigating the risks and volatility associated with our foreign currency transactions. We do not apply hedge accounting treatment to these non-designated hedging instruments. We do not hold or issue derivative instruments for trading or speculative purposes. Our foreign currency forward contracts are generally short-term in duration. Given the short duration of the forward contracts, amounts recorded generally are not significant. We account for our derivative instruments as either assets or liabilities on our Condensed Consolidated Balance Sheets and measure them at fair value. Derivatives not designated as hedging instruments are adjusted to fair value through earnings in other income (expense), net in the Condensed Consolidated Statements of Income. Recently Adopted Accounting Pronouncements On January 1, 2021, we adopted the Accounting Standards Board’s (FASB) Accounting Standards Update (ASU) 2019-12, Income Taxes (Topic 740)-Simplifying the Accounting for Income Taxes (ASU 2019-12). ASU 2019-12 simplifies the accounting for income taxes by removing certain exceptions to the general principles in Accounting Standards Codification (ASC) Topic 740, Income Taxes and clarifying and amending existing guidance. Our adoption of ASU 2019-12 did not have a significant impact on the accompanying Condensed Consolidated Financial Statements. Recent Accounting Pronouncements Not Yet Adopted There were no new accounting pronouncements issued since our filing of the Annual Report on Form 10-K for the year ended December 31, 2020, which could have a significant effect on our condensed consolidated financial statements.