CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL - USD ($) shares in Thousands, $ in Thousands	Total	General Partner	Common Stock	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Sep. 30, 2019	$ 260,840	$ (1,968)	$ 279,709	$ (16,901)
Beginning Balance, unit at Sep. 30, 2019		326	47,685
Net income	55,918	$ 377	$ 55,541
Unrealized gain on pension plan obligation	2,876			2,876
Tax effect of unrealized gain on pension plan obligation	(782)			(782)
Unrealized gain (loss) on captive insurance collateral	916			916
Tax effect of unrealized gain (loss) on captive insurance collateral	(190)			(190)
Unrealized gain (loss) on interest rate hedge	(1,193)			(1,193)
Tax effect of unrealized gain (loss) on interest rate hedge	317			317
Distributions	(24,451)	(915)	(23,536)
Retirement of units	(38,431)		$ (38,431)
Retirement of units, shares			(4,357)
Ending Balance at Sep. 30, 2020	255,820	$ (2,506)	$ 273,283	(14,957)
Ending Balance, Unit at Sep. 30, 2020		326	43,328
Net income	87,737	$ 689	$ 87,048
Unrealized gain on pension plan obligation	735			735
Tax effect of unrealized gain on pension plan obligation	(217)			(217)
Unrealized gain (loss) on captive insurance collateral	(963)			(963)
Tax effect of unrealized gain (loss) on captive insurance collateral	203			203
Unrealized gain (loss) on interest rate hedge	1,575			1,575
Tax effect of unrealized gain (loss) on interest rate hedge	(414)			(414)
Distributions	(23,448)	(1,004)	(22,444)
Retirement of units	(42,824)		$ (42,824)
Retirement of units, shares			(4,282)
Ending Balance at Sep. 30, 2021	278,204	$ (2,821)	$ 295,063	(14,038)
Ending Balance, Unit at Sep. 30, 2021		326	39,046
Net income	35,288	$ 281	$ 35,007
Unrealized gain on pension plan obligation	(436)			(436)
Tax effect of unrealized gain on pension plan obligation	129			129
Unrealized gain (loss) on captive insurance collateral	(4,952)			(4,952)
Tax effect of unrealized gain (loss) on captive insurance collateral	1,043			1,043
Unrealized gain (loss) on interest rate hedge	3,607			3,607
Tax effect of unrealized gain (loss) on interest rate hedge	(959)			(959)
Distributions	(23,192)	(1,116)	(22,076)
Retirement of units	(30,817)		$ (30,817)
Retirement of units, shares			(2,954)
Ending Balance at Sep. 30, 2022	$ 257,915	$ (3,656)	$ 277,177	$ (15,606)
Ending Balance, Unit at Sep. 30, 2022		326	36,092