Income Taxes - Schedule of Temporary Differences That Give Rise to Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Deferred tax assets:
Deferred compensation	$ 11,099	$ 11,346
Allowance for doubtful accounts	4,218	663
Accrued vacation and other	5,148	5,079
Inventory valuation	14,307	12,900
Tax loss carryforwards	18,272	17,271
Unrealized loss on financial derivatives	510
Other	1,611	1,517
Total deferred tax assets	55,165	48,776
Deferred tax liabilities:
Excess tax over book depreciation and amortization	(159,078)	(155,770)
Total deferred tax liabilities	(159,078)	(155,770)
Net deferred income tax liabilities	$ (103,913)	$ (106,994)