Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance at Dec. 31, 2016	$ 120,756	$ 25	$ 565,954	$ 0	$ (445,223)
Beginning balance (shares) at Dec. 31, 2016		24,813
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(126,817)				(126,817)
Issuance of common stock, net	290,591	$ 9	290,582
Issuance of common stock, net (shares)		9,256
Issuance of common stock upon net exercise of common stock warrants	0
Issuance of common stock upon net exercise of common stock warrants (shares)		26
Issuance of common stock under employee equity plans	10,836	$ 1	10,835
Issuance of common stock under employee equity plans (shares)		713
Stock-based compensation	6,155		6,155
Ending balance at Dec. 31, 2017	301,521	$ 35	873,526	0	(572,040)
Ending balance (shares) at Dec. 31, 2017		34,808
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(123,914)				(123,914)
Other comprehensive income, net of tax	3			3
Issuance of common stock, net	323,135	$ 7	323,128
Issuance of common stock, net (shares)		6,740
Issuance of common stock under employee equity plans	7,994		7,994
Issuance of common stock under employee equity plans (shares)		563
Shares repurchased for tax withholdings related to net share settlement of employee equity awards	(1,430)		(1,430)
Shares repurchased for tax withholdings related to net share settlement of employee equity awards (shares)		(33)
Stock-based compensation	15,492		15,492
Ending balance at Dec. 31, 2018	522,801	$ 42	1,218,710	3	(695,954)
Ending balance (shares) at Dec. 31, 2018		42,078
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(419,503)				(419,503)
Other comprehensive income, net of tax	376			376
Issuance of common stock, net	42,576	$ 1	42,575
Issuance of common stock, net (shares)		904
Issuance of common stock under employee equity plans	10,182		10,182
Issuance of common stock under employee equity plans (shares)		712
Shares repurchased for tax withholdings related to net share settlement of employee equity awards	(744)		(744)
Shares repurchased for tax withholdings related to net share settlement of employee equity awards (shares)		(17)
Issuance of common stock as consideration for asset acquisition	68,124	$ 2	68,122
Issuance of common stock in connection with asset acquisition (shares)		1,595
Stock-based compensation	21,247		21,247
Ending balance at Dec. 31, 2019	$ 245,059	$ 45	$ 1,360,092	$ 379	$ (1,115,457)
Ending balance (shares) at Dec. 31, 2019		45,272