Quarterly Information (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 25,018	$ 21,906	$ 19,983	$ 17,683	$ 21,037	$ 16,109	$ 14,277	$ 12,136	$ 12,904	$ 11,798	$ 11,419	$ 9,269	$ 84,590	$ 63,559	$ 45,390
Cost of revenue	3,229	3,168	2,991	2,878	2,674	2,678	1,717	1,617	1,138	1,182	830	891
Operating expenses	17,260	21,647	18,642	19,365	19,729	16,294	13,825	12,831	10,033	10,132	9,365	9,050
Operating income (loss)	4,529	(2,909)	(1,650)	(4,560)	(1,366)	(2,863)	(1,265)	(2,312)	1,733	484	1,224	(672)	(4,590)	(7,806)	2,769
Other income (expense), net	350	98	140	14	22	(1,351)	204	190	121	149	67	65	602	(935)	402
Income tax benefit (provision)	(1,597)	2,712	794	1,355	(783)	1,430	(99)	(3,614)	11,012	(17)	(74)	0	3,264	(3,066)	10,921
Net income (loss)	$ 3,282	$ (99)	$ (716)	$ (3,191)	$ (2,127)	$ (2,784)	$ (1,160)	$ (5,736)	$ 12,866	$ 616	$ 1,217	$ (607)	$ (724)	$ (11,807)	$ 14,092
Net income (loss) per share:
Net income (loss) per share—basic (in dollars per share)	$ 0.08	$ (0.00)	$ (0.02)	$ (0.08)					$ 0.38	$ 0.02	$ 0.04	$ (0.02)	$ (0.02)	$ (0.33)	$ 0.43
Net income (loss) per share—diluted (in dollars per share)	$ 0.08	$ (0.00)	$ (0.02)	$ (0.08)					$ 0.35	$ 0.02	$ 0.03	$ (0.02)	$ (0.02)	$ (0.33)	$ 0.40
Net income (loss) per share—basic and diluted (in dollars per share)					$ (0.06)	$ (0.08)	$ (0.03)	$ (0.17)
Shares used in calculating net income (loss) per share—basic (in shares)	40,252	39,936	38,926	38,247					33,522	33,024	32,786	32,377	39,341	35,811	33,083
Shares used in calculating net income (loss) per share—diluted (in shares)	41,635	39,936	38,926	38,247					36,251	35,610	34,815	32,377	39,341	35,811	35,537
Shares used in calculating net income (loss) per share—basic and diluted (in shares)					37,858	36,190	34,976	34,207