Nature of Operations and Summary of Significant Accounting Policies - Computation of Basic and Diluted Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	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, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net income (loss)	$ 4,996	$ 1,348	$ 909	$ 561	$ 3,282	$ (99)	$ (716)	$ (3,191)	$ (2,127)	$ (2,784)	$ (1,160)	$ (5,736)	$ 7,814	$ (724)	$ (11,807)
Weighted-average shares outstanding—basic (in shares)	41,770	41,483	41,022	40,615	40,252	39,936	38,926	38,247					41,410	39,341	35,811
Common stock equivalents (in shares)													1,123	0	0
Weighted-average shares outstanding—diluted (in shares)	43,101	42,428	42,028	41,828	41,635	39,936	38,926	38,247					42,533	39,341	35,811
Net income (loss) per share:
Basic (in dollars per share)	$ 0.12	$ 0.03	$ 0.02	$ 0.01	$ 0.08	$ 0	$ (0.02)	$ (0.08)					$ 0.19	$ (0.02)	$ (0.33)
Diluted (in dollars per share)	$ 0.12	$ 0.03	$ 0.02	$ 0.01	$ 0.08	$ 0	$ (0.02)	$ (0.08)					$ 0.18	$ (0.02)	$ (0.33)