Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Capital in Excess of Par Value	Accumulated Other Comprehensive Income/(Loss)	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance (in shares) at Dec. 31, 2017			159,524
Beginning Balance at Dec. 31, 2017	$ 87,828	$ 12,577	$ 15	$ 2,207,865	$ (2,111)	$ (2,117,941)	$ 12,577
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)			5,721
Shares issued under equity compensation plans	61,729		$ 1	61,728
Stock-based compensation	88,101			88,101
Sale of stock to Bristol-Myers Squibb (Note 10) (in shares)			8,285
Sale of stock to Bristol-Myers Squibb (Note 10)	790,232		$ 1	790,231
Comprehensive income (loss)	677,108				(4,205)	681,313
Ending Balance (in shares) at Dec. 31, 2018			173,530
Ending Balance at Dec. 31, 2018	1,717,575		$ 17	3,147,925	(6,316)	(1,424,051)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)			2,975
Shares issued under equity compensation plans	23,377			23,377
Stock-based compensation	99,795			99,795
Comprehensive income (loss)	(435,356)				5,311	(440,667)
Ending Balance (in shares) at Dec. 31, 2019			176,505
Ending Balance at Dec. 31, 2019	1,405,391		$ 17	3,271,097	(1,005)	(1,864,718)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)			3,586
Shares issued under equity compensation plans	23,373		$ 1	23,372
Stock-based compensation	94,261			94,261
Comprehensive income (loss)	(445,730)				(1,290)	(444,440)
Ending Balance (in shares) at Dec. 31, 2020			180,091
Ending Balance at Dec. 31, 2020	$ 1,077,295		$ 18	$ 3,388,730	$ (2,295)	$ (2,309,158)