Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning (in shares) at Dec. 31, 2018		160,262,000
Beginning at Dec. 31, 2018	$ 1,273,943	$ 160	$ 2,598,411	$ (40)	$ (1,324,588)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(13,329)				(13,329)
Other comprehensive income (loss)	256			256
Issuance of common stock for employee stock purchase plan (in shares)		104,000
Issuance of common stock for employee stock purchase plan	6,147	$ 0	6,147
Stock option exercises (in shares)		719,000
Stock option exercises	20,679	$ 1	20,678
Restricted stock vested during the period, net (in shares)		56,000
Restricted stock vested during the period, net	0	$ 0
Share-based compensation	25,715		25,715
Ending (in shares) at Mar. 31, 2019		161,141,000
Ending at Mar. 31, 2019	1,313,411	$ 161	2,650,951	216	(1,337,917)
Beginning (in shares) at Dec. 31, 2018		160,262,000
Beginning at Dec. 31, 2018	1,273,943	$ 160	2,598,411	(40)	(1,324,588)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(92,567)
Other comprehensive income (loss)	526
Ending (in shares) at Jun. 30, 2019		161,638,000
Ending at Jun. 30, 2019	1,271,826	$ 162	2,688,333	486	(1,417,155)
Beginning (in shares) at Mar. 31, 2019		161,141,000
Beginning at Mar. 31, 2019	1,313,411	$ 161	2,650,951	216	(1,337,917)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(79,238)				(79,238)
Other comprehensive income (loss)	270			270
Stock option exercises (in shares)		393,000
Stock option exercises	11,226	$ 1	11,225
Restricted stock vested during the period, net (in shares)		104,000
Restricted stock vested during the period, net	0	$ 0
Share-based compensation	26,157		26,157
Ending (in shares) at Jun. 30, 2019		161,638,000
Ending at Jun. 30, 2019	$ 1,271,826	$ 162	2,688,333	486	(1,417,155)
Beginning (in shares) at Dec. 31, 2019	171,994,000	171,994,000
Beginning at Dec. 31, 2019	$ 1,876,287	$ 172	3,359,124	229	(1,483,238)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(168,402)				(168,402)
Other comprehensive income (loss)	3,249			3,249
Issuance of common stock for employee stock purchase plan (in shares)		133,000
Issuance of common stock for employee stock purchase plan	8,513	$ 0	8,513
Stock option exercises (in shares)		442,000
Stock option exercises	13,273	$ 1	13,272
Restricted stock vested during the period, net (in shares)		67,000
Restricted stock vested during the period, net	0	$ 0
Share-based compensation	32,698		32,698
Ending (in shares) at Mar. 31, 2020		172,636,000
Ending at Mar. 31, 2020	$ 1,765,618	$ 173	3,413,607	3,478	(1,651,640)
Beginning (in shares) at Dec. 31, 2019	171,994,000	171,994,000
Beginning at Dec. 31, 2019	$ 1,876,287	$ 172	3,359,124	229	(1,483,238)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(189,592)
Other comprehensive income (loss)	$ 1,239
Ending (in shares) at Jun. 30, 2020	173,865,000	173,865,000
Ending at Jun. 30, 2020	$ 1,814,077	$ 174	3,485,265	1,468	(1,672,830)
Beginning (in shares) at Mar. 31, 2020		172,636,000
Beginning at Mar. 31, 2020	1,765,618	$ 173	3,413,607	3,478	(1,651,640)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(21,190)				(21,190)
Other comprehensive income (loss)	(2,010)			(2,010)
Stock option exercises (in shares)		858,000
Stock option exercises	31,485	$ 1	31,484
Restricted stock vested during the period, net (in shares)		371,000
Restricted stock vested during the period, net	0	$ 0
Share-based compensation	$ 40,174		40,174
Ending (in shares) at Jun. 30, 2020	173,865,000	173,865,000
Ending at Jun. 30, 2020	$ 1,814,077	$ 174	$ 3,485,265	$ 1,468	$ (1,672,830)