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, 2021	$ 278,204	$ (2,821)	$ 295,063	$ (14,038)
Beginning Balance, unit at Sep. 30, 2021		326	39,046
Net income	95,868	$ 819	$ 95,049
Unrealized gain on pension plan obligation	448			448
Tax effect of unrealized gain on pension plan obligation	(106)			(106)
Unrealized gain (loss) on captive insurance collateral	(2,674)			(2,674)
Tax effect of unrealized gain (loss) on captive insurance collateral	564			564
Unrealized gain (loss) on interest rate hedges	2,267			2,267
Tax effect of unrealized gain (loss) on interest rate hedges	(603)			(603)
Distributions	(11,432)	(522)	(10,910)
Retirement of units	(22,182)		$ (22,182)
Retirement of units, shares			(2,096)
Ending Balance at Mar. 31, 2022	340,354	$ (2,524)	$ 357,020	(14,142)
Ending Balance, Unit at Mar. 31, 2022		326	36,950
Beginning Balance at Dec. 31, 2021	275,359	$ (2,963)	$ 292,139	(13,817)
Beginning Balance, unit at Dec. 31, 2021		326	37,942
Net income	81,379	$ 697	$ 80,682
Unrealized gain on pension plan obligation	224			224
Tax effect of unrealized gain on pension plan obligation	(61)			(61)
Unrealized gain (loss) on captive insurance collateral	(2,062)			(2,062)
Tax effect of unrealized gain (loss) on captive insurance collateral	435			435
Unrealized gain (loss) on interest rate hedges	1,549			1,549
Tax effect of unrealized gain (loss) on interest rate hedges	(410)			(410)
Distributions	(5,642)	(258)	(5,384)
Retirement of units	(10,417)		$ (10,417)
Retirement of units, shares			(992)
Ending Balance at Mar. 31, 2022	340,354	$ (2,524)	$ 357,020	(14,142)
Ending Balance, Unit at Mar. 31, 2022		326	36,950
Beginning Balance at Sep. 30, 2022	257,915	$ (3,656)	$ 277,177	(15,606)
Beginning Balance, unit at Sep. 30, 2022		326	36,092
Ending Balance at Dec. 31, 2022	262,373	$ (3,826)	$ 281,516	(15,317)
Ending Balance, Unit at Dec. 31, 2022		326	35,681
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 (loss) on captive insurance collateral	1,130			1,130
Tax effect of unrealized gain (loss) 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 (loss) on captive insurance collateral	775			775
Tax effect of unrealized gain (loss) 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