Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Revenues
Revenues	$ 84,664	$ 82,671	$ 78,929	$ 75,343	$ 74,200	$ 71,658	$ 68,153	$ 64,878	$ 321,607	$ 278,889	$ 230,828
Cost of revenues									69,517	66,185	51,580
Gross profit									252,090	212,704	179,248
Operating expenses:
Research and development									68,239	53,255	42,816
Sales and marketing									70,833	70,039	63,855
General and administrative									40,765	39,049	35,334
Total operating expenses									179,837	162,343	142,005
Income from operations	19,545	22,549	16,108	14,051	12,943	18,117	10,895	8,406	72,253	50,361	37,243
Other income (expense), net	1,757	1,786	2,401	1,786	1,862	1,116	884	1,245	7,730	5,107	2,135
Income before income taxes	21,302	24,335	18,509	15,837	14,805	19,233	11,779	9,651	79,983	55,468	39,378
Provision for (benefit from) income taxes									10,647	(1,836)	(1,062)
Net income	$ 20,664	$ 19,174	$ 16,232	$ 13,266	$ 14,400	$ 23,469	$ 10,293	$ 9,142	$ 69,336	$ 57,304	$ 40,440
Earnings Per Share [Abstract]
Basic (in usd per share)	$ 0.53	$ 0.49	$ 0.41	$ 0.34	$ 0.37	$ 0.60	$ 0.26	$ 0.24	$ 1.77	$ 1.47	$ 1.08
Diluted (usd per share)	$ 0.50	$ 0.47	$ 0.39	$ 0.32	$ 0.35	$ 0.56	$ 0.24	$ 0.22	$ 1.68	$ 1.37	$ 1.01