Earnings Per Limited Partner Unit - Net Income Allocation and Per Unit Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Basic and Diluted Earnings Per Limited Partner:
Net income		$ 62,041	$ 81,379	$ 75,580	$ 95,868
Less General Partner's interest in net income		562	697	684	819
Net income available to limited partners		61,479	80,682	74,896	95,049
Less dilutive impact of theoretical distribution of earnings	[1]	10,990	14,707	12,714	16,599
Limited Partner's interest in net income		$ 50,489	$ 65,975	$ 62,182	$ 78,450
Per unit data:
Basic and diluted net income available to limited partners		$ 1.72	$ 2.14	$ 2.09	$ 2.49
Less dilutive impact of theoretical distribution of earnings		0.30	0.39	0.35	0.44
Limited Partner's interest in net income		$ 1.42	$ 1.75	$ 1.74	$ 2.05
Weighted average number of Limited Partner units outstanding, Basic		35,653	37,634	35,786	38,218
Weighted average number of Limited Partner units outstanding, Diluted		35,653	37,634	35,786	38,218

[1] In any accounting period where the Company’s aggregate net income exceeds its aggregate distribution for such period, the Company is required to present net income per Limited Partner unit as if all of the earnings for the period were distributed, based on the terms of the Partnership agreement, regardless of whether those earnings would actually be distributed during a particular period from an economic or practical perspective. This allocation does not impact the Company’s overall net income or other financial results.