Income Taxes - Significant Components of Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Components of Deferred Tax Assets and Liabilities [Abstract]
Accruals and reserves not currently deductible	$ 14,581	$ 18,747
Federal, state and foreign tax credits	27,923	25,413
Other assets	175	42
Equity compensation	5,926	7,615
Net operating loss carryforwards	16,790	50,882
Inventory reserves and valuation	6,520	9,847
Deferred tax assets	71,915	112,546
Depreciation and intangible amortization	(19,476)	(21,200)
Deferred tax liabilities	(19,476)	(21,200)
Valuation allowance	(18,581)	(93,402)
Net deferred tax asset	$ 33,858
Net deferred tax (liability)		$ (2,056)