Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Shares	Capital in Excess of Par Value	Accumulated Other Comprehensive Income/(Loss)	Accumulated Deficit
Beginning Balance (in shares) at Dec. 31, 2016		153,212
Beginning Balance at Dec. 31, 2016	$ 88,125	$ 15	$ 2,111,483	$ (2,363)	$ (2,021,010)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)		6,312
Shares issued under equity compensation plans	59,528		59,528
Stock-based compensation	36,615		36,615
Other comprehensive income (loss)	252		239	252	(239)
Net income (loss) (1)	(96,692)				(96,692)
Ending Balance (in shares) at Dec. 31, 2017		159,524
Ending Balance at Dec. 31, 2017	$ 87,828	$ 15	2,207,865	(2,111)	(2,117,941)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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
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
Other comprehensive income (loss)	(4,205)			(4,205)
Net income (loss) (1)	681,313				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	$ 0	23,377	0	0
Stock-based compensation	99,795		99,795	0	0
Other comprehensive income (loss)	5,311		0	5,311	0
Net income (loss) (1)	(440,667)		0	0	(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)