CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 81,379	$ 85,164	$ 95,868	$ 123,024
Other comprehensive income (loss):
Unrealized gain on pension plan obligation	224	235	448	470
Tax effect of unrealized gain on pension plan obligation	(61)	(64)	(106)	(128)
Unrealized loss on captive insurance collateral	(2,062)	(526)	(2,674)	(866)
Tax effect of unrealized loss on captive insurance collateral	435	110	564	182
Unrealized gain on interest rate hedges	1,549	719	2,267	1,051
Tax effect of unrealized gain on interest rate hedges	(410)	(190)	(603)	(278)
Total other comprehensive income (loss)	(325)	284	(104)	431
Total comprehensive income	$ 81,054	$ 85,448	$ 95,764	$ 123,455