License Agreements - Merus (Details) $ / shares in Units, $ in Thousands		1 Months Ended				12 Months Ended
	Jan. 23, 2017 USD ($) $ / shares	Jan. 31, 2021 USD ($) $ / shares shares	Feb. 28, 2017 USD ($)	Jan. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
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)
Total revenues						2,666,702	2,158,759	1,881,883
Net income (loss)						(295,697)	446,906	109,493
Current assets						2,359,894	2,481,488
Current liabilities						631,195	513,340
Merus
License agreements
Number of independent programs | item				11
Upfront payment under license agreement			$ 120,000
Research and development expense						8,900	7,200	10,300
Merus | Accrued and other liabilities
License agreements
Accrued and other liabilities						1,600	1,600
Merus | U.S.
License agreements
Profit sharing (as a percent)				50.00%
Percentage of profit (losses)				50.00%
Merus | Minimum
License agreements
Royalty payments on future global net sales (as a percent)				6.00%
Merus | Minimum | U.S.
License agreements
Royalty payments on future global net sales (as a percent)				6.00%
Merus | Minimum | Non-U.S.
License agreements
Royalty payments on future global net sales (as a percent)				6.00%
Merus | Maximum
License agreements
Royalty payments on future global net sales (as a percent)				10.00%
Percentage of reverse royalty				4.00%
Merus | Maximum | U.S.
License agreements
Royalty payments on future global net sales (as a percent)				10.00%
Percentage of additional royalties				4.00%
Merus | Maximum | Non-U.S.
License agreements
Royalty payments on future global net sales (as a percent)				10.00%
Merus | Maximum | Development and Regulatory Milestones
License agreements
Additional milestone payments under the license agreement				$ 100,000
Merus | Maximum | Sales and Commercial Milestones
License agreements
Additional milestone payments under the license agreement				$ 250,000
Merus
License agreements
Number of programs under the resulting products are co-funded for development | item				2
Associated future global development costs , if elected to co-develop (as a percent)				35.00%
Fair market value of our long term investments						$ 56,100	45,100
Ownership percentage (as a percent)						11.00%
Unrealized gain (loss) on long term investments						$ 11,000	$ 300	$ (17,300)
Merus | IPO | Subsequent Event
License agreements
Common shares purchased (in shares) | shares		350,000
Number of shares in underwritten public offering (in shares) | shares		4,848,485
Per share price | $ / shares		$ 24.75
Value of shares acquired		$ 8,700
Merus | Stock purchase agreement
License agreements
Purchase of common stock under Stock Purchase Agreement (in shares ) | shares					3,200,000
Purchase price of common stock					$ 80,000
Per share price | $ / shares	$ 24.50				$ 25.00
Discount for lack of marketability	$ 5,600
Fair value of shares on the issuance date	72,800
Total consideration paid	$ 80,000
Long term investments									$ 72,800
Research and development expense									$ 7,200