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, 2020	$ 255,820	$ (2,506)	$ 273,283	$ (14,957)
Beginning Balance, unit at Sep. 30, 2020		326	43,328
Net income	123,024	$ 977	$ 122,047
Unrealized gain on pension plan obligation	470			470
Tax effect of unrealized gain on pension plan obligation	(128)			(128)
Unrealized loss on captive insurance collateral	(866)			(866)
Tax effect of unrealized loss on captive insurance collateral	182			182
Unrealized gain on interest rate hedges	1,051			1,051
Tax effect of unrealized gain on interest rate hedges	(278)			(278)
Distributions	(11,533)	(462)	(11,071)
Retirement of units	(30,466)		$ (30,466)
Retirement of units, shares			(3,129)
Ending Balance at Mar. 31, 2021	337,276	$ (1,991)	$ 353,793	(14,526)
Ending Balance, Unit at Mar. 31, 2021		326	40,199
Beginning Balance at Dec. 31, 2020	262,616	$ (2,447)	$ 279,873	(14,810)
Beginning Balance, unit at Dec. 31, 2020		326	40,737
Net income	85,164	$ 681	$ 84,483
Unrealized gain on pension plan obligation	235			235
Tax effect of unrealized gain on pension plan obligation	(64)			(64)
Unrealized loss on captive insurance collateral	(526)			(526)
Tax effect of unrealized loss on captive insurance collateral	110			110
Unrealized gain on interest rate hedges	719			719
Tax effect of unrealized gain on interest rate hedges	(190)			(190)
Distributions	(5,594)	(225)	(5,369)
Retirement of units	(5,194)		$ (5,194)
Retirement of units, shares			(538)
Ending Balance at Mar. 31, 2021	337,276	$ (1,991)	$ 353,793	(14,526)
Ending Balance, Unit at Mar. 31, 2021		326	40,199
Beginning Balance at Sep. 30, 2021	278,204	$ (2,821)	$ 295,063	(14,038)
Beginning Balance, unit at Sep. 30, 2021		326	39,046
Ending Balance at Dec. 31, 2021	275,359	$ (2,963)	$ 292,139	(13,817)
Ending Balance, Unit at Dec. 31, 2021		326	37,942
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 loss on captive insurance collateral	(2,674)			(2,674)
Tax effect of unrealized loss on captive insurance collateral	564			564
Unrealized gain on interest rate hedges	2,267			2,267
Tax effect of unrealized gain 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 loss on captive insurance collateral	(2,062)			(2,062)
Tax effect of unrealized loss on captive insurance collateral	435			435
Unrealized gain on interest rate hedges	1,549			1,549
Tax effect of unrealized gain 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