License Agreements - Calithera (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions		1 Months Ended	12 Months Ended
	Jan. 30, 2017	Jan. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2020	Jan. 01, 2017
License agreements
Long term investments			$ 222,301	$ 133,657
Research and development expense			2,215,942	1,154,111	$ 1,197,957
Unrealized gain (loss) on long term investments			10,426	34,458	(44,093)
Calithera
License agreements
Funding of future development costs (as a percent)		70.00%
Upfront payment made under license agreement		$ 45,000
Potential milestone payments to be made with profit sharing in effect		430,000
Potential milestone payments to be made with profit sharing terminated		$ 750,000					$ 738,000
Milestone payment made under license agreement						$ 12,000
Research and development expense			8,900	17,900	12,000
Calithera | Accrued and other liabilities
License agreements
Accrued and other liabilities			600	1,100
Calithera | U.S.
License agreements
Percentage of profit (losses)		60.00%
Calithera
License agreements
Total consideration paid	$ 53,000	$ 53,000
Long term investments			$ 8,400	9,800
Ownership percentage (as a percent)			2.00%
Calithera | Other Comprehensive Income
License agreements
Unrealized gain (loss) on long term investments			$ 1,400	$ 2,900	$ (7,500)
Calithera | Stock purchase agreement
License agreements
Purchase of common stock under Stock Purchase Agreement (in shares )		1.7
Purchase price of common stock								$ 8,000
Per share price	$ 6.75							$ 4.65
Fair market value of our long term investments	$ 11,600
Stock purchase price		$ 8,000
Long term investments						11,600
Research and development expense						$ 41,400
Calithera | Collaboration and license agreement
License agreements
Upfront license fees		$ 45,000