Income Taxes - Income Taxes Computed Using Federal Income Tax Rate (Details) - USD ($) $ 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
Income Tax Disclosure [Abstract]
Amount computed using statutory rate													$ 841	$ 2,122	$ (1,078)
Net change in valuation allowance for net deferred tax assets													(459)	(367)	10,058
AMT and other													0	(191)	20
Foreign rate differential													664	22	(169)
Non-deductible items													(151)	(276)	(370)
State income tax													(370)	50	(34)
Impact of tax reform on deferred taxes													0	(4,901)	0
Research and development credits													1,694	475	2,494
Foreign income tax													(494)	0	0
Stock compensation, net													1,539	0	0
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