CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 37,860	$ 27,755
Other comprehensive income:
Unrealized gain on pension plan obligation	235	455
Tax effect of unrealized gain on pension plan obligation	(64)	(125)
Unrealized loss on captive insurance collateral	(340)	(64)
Tax effect of unrealized loss on captive insurance collateral	72	8
Unrealized gain on interest rate hedges	332	334
Tax effect of unrealized gain on interest rate hedges	(88)	(86)
Total other comprehensive income	147	522
Total comprehensive income	$ 38,007	$ 28,277