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, 2019	$ 260,840	$ (1,968)	$ 279,709	$ (16,901)
Beginning Balance, unit at Sep. 30, 2019		326	47,685
Net income (loss)	86,117	$ 600	$ 85,517
Unrealized gain on pension plan obligation	1,365			1,365
Tax effect of unrealized gain on pension plan obligation	(385)			(385)
Unrealized gain (loss) on captive insurance collateral	1,029			1,029
Tax effect of unrealized gain (loss) on captive insurance collateral	(214)			(214)
Unrealized gain (loss) on interest rate hedges	(1,508)			(1,508)
Tax effect of unrealized gain (loss) on interest rate hedges	408			408
Distributions	(18,389)	(673)	(17,716)
Retirement of units	(27,988)		$ (27,988)
Retirement of units, shares			(3,218)
Ending Balance at Jun. 30, 2020	301,275	$ (2,041)	$ 319,522	(16,206)
Ending Balance, Unit at Jun. 30, 2020		326	44,467
Beginning Balance at Mar. 31, 2020	315,955	$ (1,792)	$ 334,968	(17,221)
Beginning Balance, unit at Mar. 31, 2020		326	45,622
Net income (loss)	(46)	$ (1)	$ (45)
Unrealized gain on pension plan obligation	455			455
Tax effect of unrealized gain on pension plan obligation	(127)			(127)
Unrealized gain (loss) on captive insurance collateral	986			986
Tax effect of unrealized gain (loss) on captive insurance collateral	(207)			(207)
Unrealized gain (loss) on interest rate hedges	(126)			(126)
Tax effect of unrealized gain (loss) on interest rate hedges	34			34
Distributions	(6,236)	(248)	(5,988)
Retirement of units	(9,413)		$ (9,413)
Retirement of units, shares			(1,155)
Ending Balance at Jun. 30, 2020	301,275	$ (2,041)	$ 319,522	(16,206)
Ending Balance, Unit at Jun. 30, 2020		326	44,467
Beginning Balance at Sep. 30, 2020	255,820	$ (2,506)	$ 273,283	(14,957)
Beginning Balance, unit at Sep. 30, 2020		326	43,328
Net income (loss)	110,970	$ 879	$ 110,091
Unrealized gain on pension plan obligation	704			704
Tax effect of unrealized gain on pension plan obligation	(193)			(193)
Unrealized gain (loss) on captive insurance collateral	(913)			(913)
Tax effect of unrealized gain (loss) on captive insurance collateral	193			193
Unrealized gain (loss) on interest rate hedges	1,303			1,303
Tax effect of unrealized gain (loss) on interest rate hedges	(344)			(344)
Distributions	(17,535)	(735)	(16,800)
Retirement of units	(36,682)		$ (36,682)
Retirement of units, shares			(3,697)
Ending Balance at Jun. 30, 2021	313,323	$ (2,362)	$ 329,892	(14,207)
Ending Balance, Unit at Jun. 30, 2021		326	39,631
Beginning Balance at Mar. 31, 2021	337,276	$ (1,991)	$ 353,793	(14,526)
Beginning Balance, unit at Mar. 31, 2021		326	40,199
Net income (loss)	(12,054)	$ (98)	$ (11,956)
Unrealized gain on pension plan obligation	234			234
Tax effect of unrealized gain on pension plan obligation	(65)			(65)
Unrealized gain (loss) on captive insurance collateral	(47)			(47)
Tax effect of unrealized gain (loss) on captive insurance collateral	11			11
Unrealized gain (loss) on interest rate hedges	252			252
Tax effect of unrealized gain (loss) on interest rate hedges	(66)			(66)
Distributions	(6,002)	(273)	(5,729)
Retirement of units	(6,216)		$ (6,216)
Retirement of units, shares			(568)
Ending Balance at Jun. 30, 2021	$ 313,323	$ (2,362)	$ 329,892	$ (14,207)
Ending Balance, Unit at Jun. 30, 2021		326	39,631