Consolidated Statements of Stockholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings (Accumulated Deficit) [Member]
Beginning balance (in shares) at Dec. 31, 2016		225,663,277
Beginning balance at Dec. 31, 2016	$ 998,532	$ 23	$ 859,345	$ (978)	$ 140,142
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		13,093,245
Issuance of common stock	19,011	$ 1	19,010
Stock-based compensation expense	92,081		92,081
Taxes related to net share settlement of restricted stock units	(14,376)		(14,376)
Net Income (Loss) Attributable to Parent	(277,192)				(277,192)
Other comprehensive income	969			969
Ending balance (in shares) at Dec. 31, 2017		238,756,522
Ending balance at Dec. 31, 2017	823,963	$ 24	956,060	(9)	(132,112)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		13,606,319
Issuance of common stock	21,470	$ 1	21,469
Stock-based compensation expense	96,953		96,953
Taxes related to net share settlement of restricted stock units	(19,436)		(19,436)
Net Income (Loss) Attributable to Parent	(185,829)				(185,829)
Other comprehensive income	(57)			(57)
Ending balance (in shares) at Dec. 31, 2018		252,362,841
Ending balance at Dec. 31, 2018	735,938	$ 25	1,055,046	(66)	(319,067)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		12,520,585
Issuance of common stock	13,019	$ 1	13,018
Stock-based compensation expense	76,934		76,934
Taxes related to net share settlement of restricted stock units	(18,171)		(18,171)
Net Income (Loss) Attributable to Parent	(320,711)				(320,711)
Other comprehensive income	254			254
Ending balance (in shares) at Dec. 31, 2019		264,883,426
Ending balance at Dec. 31, 2019	$ 487,263	$ 26	$ 1,126,827	$ 188	$ (639,778)