Supplementary Financial Data (Unaudited) - Supplementary Financial Data (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Net revenue	$ 51,795	$ 46,117	$ 47,774	$ 36,026	$ 45,469	$ 40,573	$ 42,553	$ 34,125
Cost of revenue	23,005	19,884	21,943	18,717	26,683	18,688	20,176	16,791
Gross profit	28,790	26,233	25,831	17,309	18,786	21,885	22,377	17,334	$ 98,163	$ 80,382		$ 86,110
Sales and marketing	20,323	17,691	16,992	16,104	15,318	14,479	15,535	13,088	71,109	58,420		52,070
Research and development	4,463	3,643	3,273	3,706	3,464	3,244	4,095	3,556	15,085	14,359		12,874
General and administrative	5,933	7,308	5,267	5,525	5,494	5,160	4,902	5,439	24,033	20,995		14,090
Total operating expenses	30,719	28,642	25,532	25,335	24,276	22,883	24,532	22,083	110,227	93,774		75,034
Income (loss) from operations	(1,929)	(2,409)	299	(8,026)	(5,490)	(998)	(2,155)	(4,749)	(12,064)	(13,392)		11,076
Interest and other income, net	(20)	(146)	46	(79)	(44)	(49)	(129)	98	(199)	(123)	[1]	884
Income (loss) before income taxes	(1,949)	(2,555)	345	(8,105)	(5,534)	(1,047)	(2,284)	(4,651)	(12,263)	(13,515)		11,960
Income tax provision (benefit)	139	73	(243)	115	20,760	(174)	(712)	(2,619)	85	17,255		(18,033)
Net income (loss)	$ (2,088)	$ (2,628)	$ 588	$ (8,220)	$ (26,293)	$ (873)	$ (1,572)	$ (2,032)	$ (12,348)	$ (30,770)		$ 29,993
Net income (loss) per share-basic (in dollars per share)	$ (0.15)	$ (0.19)	$ 0.04	$ (0.59)	$ (1.89)	$ (0.06)	$ (0.11)	$ (0.15)	$ (0.88)	$ (2.23)		$ 2.16
Net income (loss) per share-diluted (in dollars per share)	$ (0.15)	$ (0.19)	$ 0.04	$ (0.59)	$ (1.89)	$ (0.06)	$ (0.11)	$ (0.15)	$ (0.88)	$ (2.23)		$ 2.04
Basic (in shares)	14,261	14,182	14,086	14,017	13,932	13,851	13,709	13,587	14,096	13,771		13,873
Diluted (in shares)	14,261	14,182	14,356	14,017	13,932	13,851	13,709	13,587	14,096	13,771		14,728

[1] Included in interest and other income, net, is the estimated interest expense for advance payment related to service contracts under the new revenue standard.