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, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Basic and Diluted Earnings Per Limited Partner:
Net income		$ 68,374	$ 62,041	$ 81,353	$ 75,580
Less General Partner's interest in net income		620	562	738	684
Net income available to limited partners		67,754	61,479	80,615	74,896
Less dilutive impact of theoretical distribution of earnings	[1]	12,164	10,990	13,752	12,714
Limited Partner's interest in net income		$ 55,590	$ 50,489	$ 66,863	$ 62,182
Per unit data:
Basic net income available to limited partners		$ 1.91	$ 1.72	$ 2.27	$ 2.09
Diluted net income available to limited partners		1.91	1.72	2.27	2.09
Less dilutive impact of theoretical distribution of earnings	[1]	0.35	0.3	0.39	0.35
Limited Partner's interest in net income	[2]	$ 1.56	$ 1.42	$ 1.88	$ 1.74
Weighted average number of Limited Partner units outstanding, Basic		35,549	35,653	35,571	35,786
Weighted average number of Limited Partner units outstanding, Diluted		35,549	35,653	35,571	35,786

[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.

[2] See Note 15 - Earnings Per Limited Partner Unit.