Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues
Revenues	$ 52,224	$ 50,987	$ 48,466	$ 46,248	$ 44,445	$ 42,469	$ 39,877	$ 37,493	$ 197,925	$ 164,284	$ 133,579
Cost of revenues	11,677	11,288	10,092	9,416	9,002	8,762	8,157	7,964	42,473	33,885	28,963
Gross profit	40,547	39,699	38,374	36,832	35,443	33,707	31,720	29,529	155,452	130,399	104,616
Operating expenses:
Research and development	8,885	9,405	9,143	7,834	7,532	7,564	7,205	7,150	35,267	29,451	26,320
Sales and marketing	15,346	14,240	14,451	13,933	13,068	12,282	12,776	11,443	57,970	49,569	48,049
General and administrative	7,505	8,067	9,068	7,468	7,147	6,983	6,427	6,016	32,108	26,573	21,000
Total operating expenses	31,736	31,712	32,662	29,235	27,747	26,829	26,408	24,609	125,345	105,593	95,369
Income from operations	8,811	7,987	5,712	7,597	7,696	6,878	5,312	4,920	30,107	24,806	9,247
Other income (expense), net	(116)	230	40	168	(183)	(154)	128	(77)	322	(286)	(634)
Income before income taxes	8,695	8,217	5,752	7,765	7,513	6,724	5,440	4,843	30,429	24,520	8,613
Provision for (benefit from) income taxes	2,788	3,221	2,214	2,982	2,089	2,601	2,124	1,841	11,205	8,655	(21,631)
Net income	$ 5,907	$ 4,996	$ 3,538	$ 4,783	$ 5,424	$ 4,123	$ 3,316	$ 3,002	$ 19,224	$ 15,865	$ 30,244
Earnings Per Share [Abstract]
Basic (in usd per share)	$ 0.17	$ 0.14	$ 0.10	$ 0.14	$ 0.16	$ 0.12	$ 0.10	$ 0.09	$ 0.55	$ 0.47	$ 0.92
Diluted (usd per share)	$ 0.15	$ 0.13	$ 0.09	$ 0.13	$ 0.14	$ 0.11	$ 0.09	$ 0.08	$ 0.50	$ 0.42	$ 0.81