Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Deferred tax assets:
Federal and state tax carryforwards	$ 192,981	$ 208,360
Inventory adjustments	34,971	42,605
Intangible assets	13,993	17,209
Incentive compensation	13,116	9,360
Warranty and other reserves	5,503	4,302
Property, equipment and other assets	2,197	2,255
Uncertain tax positions	723	729
Other	844	623
Total deferred tax assets	264,328	285,443
Valuation allowance	(39,185)	(38,486)
Net deferred tax assets	$ 225,143	$ 246,957