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, 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
Beginning Balance at Sep. 30, 2024	263,893	$ (5,714)	$ 282,058	(12,451)
Beginning Balance, unit at Sep. 30, 2024		326	34,587
Ending Balance at Dec. 31, 2024	291,042	$ (5,775)	$ 308,528	(11,711)
Ending Balance, Unit at Dec. 31, 2024		326	34,574
Beginning Balance at Sep. 30, 2024	263,893	$ (5,714)	$ 282,058	(12,451)
Beginning Balance, unit at Sep. 30, 2024		326	34,587
Net income	118,795	$ 1,109	$ 117,686
Unrealized gain on pension plan obligation	864			864
Tax effect of unrealized gain on pension plan obligation	(228)			(228)
Unrealized gain on captive insurance collateral	171			171
Tax effect of unrealized gain on captive insurance collateral	(36)			(36)
Unrealized gain (loss) on interest rate hedges	(3)			(3)
Tax effect of unrealized gain (loss) on interest rate hedges	1			1
Distributions	(12,664)	(735)	(11,929)
Retirement of units	(212)		$ (212)
Retirement of units, shares			(19)
Ending Balance at Mar. 31, 2025	370,581	$ (5,340)	$ 387,603	(11,682)
Ending Balance, Unit at Mar. 31, 2025		326	34,568
Beginning Balance at Dec. 31, 2024	291,042	$ (5,775)	$ 308,528	(11,711)
Beginning Balance, unit at Dec. 31, 2024		326	34,574
Net income	85,911	$ 802	$ 85,109
Unrealized gain on pension plan obligation	432			432
Tax effect of unrealized gain on pension plan obligation	(33)			(33)
Unrealized gain on captive insurance collateral	125			125
Tax effect of unrealized gain on captive insurance collateral	(27)			(27)
Unrealized gain (loss) on interest rate hedges	(636)			(636)
Tax effect of unrealized gain (loss) on interest rate hedges	168			168
Distributions	(6,330)	(367)	(5,963)
Retirement of units	(71)		$ (71)
Retirement of units, shares			(6)
Ending Balance at Mar. 31, 2025	$ 370,581	$ (5,340)	$ 387,603	$ (11,682)
Ending Balance, Unit at Mar. 31, 2025		326	34,568