Consolidated Statement of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2017	$ 60,699	$ 40	$ 324,376	$ (263,571)	$ (146)
Beginning balance, shares at Dec. 31, 2017		40,571,015
Issuance of common stock upon exercise of stock options, value	32		32
Issuance of common stock upon exercise of stock options, shares		48,053
Issuance of common stock upon vesting of RSUs, net of tax witholdings, shares		51,500
Repurchase of common stock for employee tax witholdings, value	(197)		(197)
Repurchase of common stock for employee tax witholdings, shares		(17,900)
Stock-based compensation expense	4,236		4,236
Unrealized gain on investments	40				40
Adoption of new revenue standard (ASC 606)	(26,857)			(26,857)
Net loss	(27,919)			(27,919)
Ending balance at Mar. 31, 2018	10,034	$ 40	328,447	(318,347)	$ (106)
Ending balance, shares at Mar. 31, 2018		40,652,668
Beginning balance at Dec. 31, 2018	$ (48,045)	$ 41	341,284	(389,370)
Beginning balance, shares at Dec. 31, 2018	40,936,735	40,936,735
Issuance of common stock upon exercise of stock options, value	$ 120		120
Issuance of common stock upon exercise of stock options, shares	38,125	38,125
Issuance of common stock upon vesting of RSUs, value	$ 153		153
Issuance of common stock upon vesting of RSUs, shares		73,500
Issuance of common stock under ESPP plan, value	207		207
Issuance of common stock under ESPP plan, shares		46,472
Stock-based compensation expense	2,065		2,065
Net loss	(24,333)			(24,333)
Ending balance at Mar. 31, 2019	$ (69,833)	$ 41	$ 343,829	$ (413,703)
Ending balance, shares at Mar. 31, 2019	41,094,832	41,094,832