Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2016	$ 132,631	$ 40	$ 306,931	$ (149)	$ (174,191)
Beginning balance, shares at Dec. 31, 2016		40,355,753
Issuance of common stock upon exercise of stock options, value	116		116
Issuance of common stock upon exercise of stock options, shares		174,386
Issuance of common stock upon vesting of RSUs, net of tax withholdings, value	(33)		(33)
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		40,876
Stock-based compensation expense	17,362		17,362
Unrealized gain (loss) on investments	3			3
Net loss	(89,380)				(89,380)
Ending balance at Dec. 31, 2017	60,699	$ 40	324,376	(146)	(263,571)
Ending balance, shares at Dec. 31, 2017		40,571,015
Issuance of common stock upon exercise of stock options, value	147	$ 1	146
Issuance of common stock upon exercise of stock options, shares		212,240
Issuance of common stock upon vesting of RSUs, net of tax withholdings, value	61		61
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		138,048
Repurchase of common stock for employee tax withholdings, value	(197)		(197)
Repurchase of common stock for employee tax withholdings, shares		(17,900)
Issuance of common stock under ESPP plan, value	257		257
Issuance of common stock under ESPP plan, shares		33,332
Stock-based compensation expense	16,641		16,641
Unrealized gain (loss) on investments	146			$ 146
Adoption of new revenue standard (ASC 606)	(26,857)				(26,857)
Net loss	(98,942)				(98,942)
Ending balance at Dec. 31, 2018	$ (48,045)	$ 41	341,284		(389,370)
Ending balance, shares at Dec. 31, 2018	40,936,735	40,936,735
Issuance of common stock from public offering, net of commissions, underwriting discounts and offering costs, value	$ 60,527	$ 29	60,498
Issuance of common stock from public offering, net of commissions, underwriting discounts and offering costs, shares		28,818,578
Issuance of common stock from at the market equity offering, value	512		512
Issuance of common stock from at the market equity offering, shares		128,400
Issuance of common stock upon exercise of stock options, value	$ 145		145
Issuance of common stock upon exercise of stock options, shares	90,125	90,125
Issuance of common stock upon vesting of RSUs, net of tax withholdings, value	$ 176		176
Issuance of common stock upon vesting of RSUs, net of tax withholdings, shares		94,400
Issuance of common stock under ESPP plan, value	296		296
Issuance of common stock under ESPP plan, shares		75,014
Stock-based compensation expense	8,344		8,344
Net loss	(70,279)				(70,279)
Ending balance at Dec. 31, 2019	$ (48,324)	$ 70	$ 411,255		$ (459,649)
Ending balance, shares at Dec. 31, 2019	70,143,252	70,143,252