CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 87,737	$ 55,918	$ 17,637
Other comprehensive income:
Unrealized gain on pension plan obligation	735	2,876	1,170
Tax effect of unrealized gain on pension plan obligation	(217)	(782)	(320)
Unrealized gain (loss) on captive insurance collateral	(963)	916	2,231
Tax effect of unrealized gain (loss) on captive insurance collateral	203	(190)	(473)
Unrealized gain (loss) on interest rate hedge	1,575	(1,193)	(1,993)
Tax effect of unrealized gain (loss) on interest rate hedge	(414)	317	525
Total other comprehensive income	919	1,944	1,140
Total comprehensive income	$ 88,656	$ 57,862	$ 18,777