Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Beginning balance at Dec. 31, 2016	$ 227,220	$ 7	$ 420,897	$ (1,684)	$ (192,000)
Beginning balance, Shares at Dec. 31, 2016		67,918,246
Issuance of common stock upon exercise of stock options	2,304		2,304
Issuance of common stock upon exercise of stock options, Shares		2,041,862
Issuance of common stock upon exercise of warrants	40		40
Issuance of common stock upon exercise of warrants, Shares		28,243
Issuance of common stock under Employee Stock Purchase Plan	828		828
Issuance of common stock under Employee Stock Purchase Plan, Shares		103,562
Issuance of common stock upon at the market offering	78,991	$ 1	78,990
Issuance of common stock upon at the market offering (in shares)		7,494,438
Release of restricted stock units		149,850
Stock-based compensation	16,376		16,376
Other comprehensive income (loss)	3,577			3,577
Net loss	(91,863)				(91,863)
Ending balance at Dec. 31, 2017	237,473	$ 8	519,435	1,893	(283,863)
Ending balance, Shares at Dec. 31, 2017		77,736,201
Issuance of common stock upon exercise of stock options	1,457		1,457
Issuance of common stock upon exercise of stock options, Shares		1,404,422
Issuance of common stock upon exercise of warrants, Shares		3,317
Issuance of common stock under Employee Stock Purchase Plan	529		529
Issuance of common stock under Employee Stock Purchase Plan, Shares		111,321
Release of restricted stock units		316,453
Stock-based compensation	17,474		17,474
Other comprehensive income (loss)	(953)			(953)
Cumulative effect of changes in accounting principles related to revenue recognition	(25,312)				(25,312)
Net loss	(95,357)				(95,357)
Ending balance at Dec. 31, 2018	$ 135,311	$ 8	538,895	940	(404,532)
Ending balance, Shares at Dec. 31, 2018	79,571,714	79,571,714
Issuance of common stock upon exercise of stock options	$ 530		530
Issuance of common stock upon exercise of stock options, Shares	548,523	548,523
Issuance of common stock under Employee Stock Purchase Plan	$ 213		213
Issuance of common stock under Employee Stock Purchase Plan, Shares		111,331
Release of restricted stock units		504,120
Stock-based compensation	12,439		12,439
Other comprehensive income (loss)	(526)			(526)
Net loss	(82,372)				(82,372)
Ending balance at Dec. 31, 2019	$ 65,595	$ 8	$ 552,077	$ 414	$ (486,904)
Ending balance, Shares at Dec. 31, 2019	80,735,688	80,735,688