Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Deferred Tax Assets, Gross [Abstract]
Accruals and reserves not currently deductible	$ 14,286	$ 11,699
Federal, state and foreign tax credits	5,952	27,923
Other assets	2,487	175
Equity compensation	5,360	5,926
Net operating loss carryforwards	18,987	16,790
Deferred revenue	4,038	2,882
Inventory reserves and valuation	5,626	6,520
Deferred tax assets	$ 56,736	$ 71,915