Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Deferred tax assets:
Federal and state tax carryforwards	$ 208,360	$ 196,702
Inventory adjustments	42,605	29,565
Intangible assets	17,209	192
Incentive compensation	9,360	11,959
Warranty and other reserves	4,302	6,350
Property, equipment and other assets	2,255	2,123
Uncertain tax positions	729	734
Other	623	542
Total deferred tax assets	285,443	248,167
Valuation allowance	(38,486)	(34,212)
Net deferred tax assets	$ 246,957	$ 213,955