CONDENSED CONSOLIDATED STATEMENT OF PARTNERS' CAPITAL - USD ($) shares in Thousands, $ in Thousands	Total	General Partner	Common Stock	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Sep. 30, 2022	$ 257,915	$ (3,656)	$ 277,177	$ (15,606)
Beginning Balance, unit at Sep. 30, 2022		326	36,092
Net income	75,580	$ 684	$ 74,896
Unrealized gain on pension plan obligation	762			762
Tax effect of unrealized gain on pension plan obligation	(201)			(201)
Unrealized gain on captive insurance collateral	1,130			1,130
Tax effect of unrealized gain on captive insurance collateral	(238)			(238)
Unrealized gain (loss) on interest rate hedges	(1,081)			(1,081)
Tax effect of unrealized gain (loss) on interest rate hedges	288			288
Distributions	(11,505)	(581)	(10,924)
Retirement of units	(4,475)		$ (4,475)
Retirement of units, shares			(489)
Ending Balance at Mar. 31, 2023	318,175	$ (3,553)	$ 336,674	(14,946)
Ending Balance, Unit at Mar. 31, 2023		326	35,603
Beginning Balance at Dec. 31, 2022	262,373	$ (3,826)	$ 281,516	(15,317)
Beginning Balance, unit at Dec. 31, 2022		326	35,681
Net income	62,041	$ 562	$ 61,479
Unrealized gain on pension plan obligation	382			382
Tax effect of unrealized gain on pension plan obligation	(104)			(104)
Unrealized gain on captive insurance collateral	775			775
Tax effect of unrealized gain on captive insurance collateral	(164)			(164)
Unrealized gain (loss) on interest rate hedges	(704)			(704)
Tax effect of unrealized gain (loss) on interest rate hedges	186			186
Distributions	(5,731)	(289)	(5,442)
Retirement of units	(879)		$ (879)
Retirement of units, shares			(78)
Ending Balance at Mar. 31, 2023	318,175	$ (3,553)	$ 336,674	(14,946)
Ending Balance, Unit at Mar. 31, 2023		326	35,603
Beginning Balance at Sep. 30, 2023	263,724	$ (4,615)	$ 281,862	(13,523)
Beginning Balance, unit at Sep. 30, 2023		326	35,603
Ending Balance at Dec. 31, 2023	270,652	$ (4,831)	$ 288,789	(13,306)
Ending Balance, Unit at Dec. 31, 2023		326	35,590
Beginning Balance at Sep. 30, 2023	263,724	$ (4,615)	$ 281,862	(13,523)
Beginning Balance, unit at Sep. 30, 2023		326	35,603
Net income	81,353	$ 738	$ 80,615
Unrealized gain on pension plan obligation	638			638
Tax effect of unrealized gain on pension plan obligation	(160)			(160)
Unrealized gain on captive insurance collateral	1,195			1,195
Tax effect of unrealized gain on captive insurance collateral	(252)			(252)
Unrealized gain (loss) on interest rate hedges	(821)			(821)
Tax effect of unrealized gain (loss) on interest rate hedges	220			220
Distributions	(12,234)	(667)	(11,567)
Retirement of units	(2,528)		$ (2,528)
Retirement of units, shares			(231)
Ending Balance at Mar. 31, 2024	331,135	$ (4,544)	$ 348,382	(12,703)
Ending Balance, Unit at Mar. 31, 2024		326	35,372
Beginning Balance at Dec. 31, 2023	270,652	$ (4,831)	$ 288,789	(13,306)
Beginning Balance, unit at Dec. 31, 2023		326	35,590
Net income	68,374	$ 620	$ 67,754
Unrealized gain on pension plan obligation	319			319
Tax effect of unrealized gain on pension plan obligation	(85)			(85)
Unrealized gain on captive insurance collateral	263			263
Tax effect of unrealized gain on captive insurance collateral	(50)			(50)
Unrealized gain (loss) on interest rate hedges	221			221
Tax effect of unrealized gain (loss) on interest rate hedges	(65)			(65)
Distributions	(6,116)	(333)	(5,783)
Retirement of units	(2,378)		$ (2,378)
Retirement of units, shares			(218)
Ending Balance at Mar. 31, 2024	$ 331,135	$ (4,544)	$ 348,382	$ (12,703)
Ending Balance, Unit at Mar. 31, 2024		326	35,372