Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ 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
Beginning at Dec. 31, 2018	$ 1,273,943	$ 160	$ 2,598,411	$ (40)	$ (1,324,588)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(13,329)				(13,329)
Other comprehensive income (loss)	256			256
Issuance of common stock for employee stock purchase plan (in shares)		104
Issuance of common stock for employee stock purchase plan	6,147	$ 0	6,147
Stock option exercises (in shares)		719
Stock option exercises	20,679	$ 1	20,678
Restricted stock vested during the period, net (in shares)		56
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
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
Beginning at Dec. 31, 2018	1,273,943	$ 160	2,598,411	(40)	(1,324,588)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(184,480)
Other comprehensive income (loss)	342
Ending (in shares) at Sep. 30, 2019		171,108
Ending at Sep. 30, 2019	1,779,601	$ 171	3,288,196	302	(1,509,068)
Beginning (in shares) at Mar. 31, 2019		161,141
Beginning at Mar. 31, 2019	1,313,411	$ 161	2,650,951	216	(1,337,917)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(79,238)				(79,238)
Other comprehensive income (loss)	270			270
Stock option exercises (in shares)		393
Stock option exercises	11,226	$ 1	11,225
Restricted stock vested during the period, net (in shares)		104
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
Ending at Jun. 30, 2019	1,271,826	$ 162	2,688,333	486	(1,417,155)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(91,913)				(91,913)
Other comprehensive income (loss)	(184)			(184)
Issuance of common stock for employee stock purchase plan (in shares)		85
Issuance of common stock for employee stock purchase plan	5,452	$ 0	5,452
Stock option exercises (in shares)		513
Stock option exercises	17,854	$ 0	17,854
Restricted stock vested during the period, net (in shares)		658
Restricted stock vested during the period, net	0	$ 1	(1)
Share-based compensation	27,875		27,875
Issuance of common stock (in shares)		8,214
Issuance of common stock	548,691	$ 8	548,683
Ending (in shares) at Sep. 30, 2019		171,108
Ending at Sep. 30, 2019	$ 1,779,601	$ 171	3,288,196	302	(1,509,068)
Beginning (in shares) at Dec. 31, 2019	171,994	171,994
Beginning at Dec. 31, 2019	$ 1,876,287	$ 172	3,359,124	229	(1,483,238)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (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
Issuance of common stock for employee stock purchase plan	8,513	$ 0	8,513
Stock option exercises (in shares)		442
Stock option exercises	13,273	$ 1	13,272
Restricted stock vested during the period, net (in shares)		67
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
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	171,994
Beginning at Dec. 31, 2019	$ 1,876,287	$ 172	3,359,124	229	(1,483,238)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	446,575
Other comprehensive income (loss)	$ 621
Ending (in shares) at Sep. 30, 2020	175,188	175,188
Ending at Sep. 30, 2020	$ 2,258,030	$ 175	3,293,668	850	(1,036,663)
Beginning (in shares) at Mar. 31, 2020		172,636
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 income (loss)	(21,190)				(21,190)
Other comprehensive income (loss)	(2,010)			(2,010)
Stock option exercises (in shares)		858
Stock option exercises	31,485	$ 1	31,484
Restricted stock vested during the period, net (in shares)		371
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
Ending at Jun. 30, 2020	1,814,077	$ 174	3,485,265	1,468	(1,672,830)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	636,167				636,167
Other comprehensive income (loss)	(618)			(618)
Issuance of common stock for employee stock purchase plan (in shares)		75
Issuance of common stock for employee stock purchase plan	6,948	$ 0	6,948
Stock option exercises (in shares)		352
Stock option exercises	12,554	$ 0	12,554
Restricted stock vested during the period, net (in shares)		896
Restricted stock vested during the period, net	0	$ 1	(1)
Share-based compensation	39,052		39,052
Premium for commitment to sell common stock	$ (250,150)		(250,150)
Ending (in shares) at Sep. 30, 2020	175,188	175,188
Ending at Sep. 30, 2020	$ 2,258,030	$ 175	$ 3,293,668	$ 850	$ (1,036,663)