CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (12,054)	$ (46)	$ 110,970	$ 86,117
Other comprehensive income:
Unrealized gain on pension plan obligation	234	455	704	1,365
Tax effect of unrealized gain on pension plan obligation	(65)	(127)	(193)	(385)
Unrealized gain (loss) on captive insurance collateral	(47)	986	(913)	1,029
Tax effect of unrealized gain (loss) on captive insurance collateral	11	(207)	193	(214)
Unrealized gain (loss) on interest rate hedges	252	(126)	1,303	(1,508)
Tax effect of unrealized gain (loss) on interest rate hedges	(66)	34	(344)	408
Total other comprehensive income	319	1,015	750	695
Total comprehensive income (loss)	$ (11,735)	$ 969	$ 111,720	$ 86,812