CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 85,164	$ 58,408	$ 123,024	$ 86,163
Other comprehensive income:
Unrealized gain on pension plan obligation	235	455	470	910
Tax effect of unrealized gain on pension plan obligation	(64)	(133)	(128)	(258)
Unrealized gain (loss) on captive insurance collateral	(526)	107	(866)	43
Tax effect of unrealized gain (loss) on captive insurance collateral	110	(15)	182	(7)
Unrealized gain (loss) on interest rate hedges	719	(1,716)	1,051	(1,382)
Tax effect of unrealized gain (loss) on interest rate hedges	(190)	460	(278)	374
Total other comprehensive income (loss)	284	(842)	431	(320)
Total comprehensive income	$ 85,448	$ 57,566	$ 123,455	$ 85,843