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, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Basic and Diluted Earnings Per Limited Partner:
Net income		$ 85,911	$ 68,374	$ 118,795	$ 81,353
Less General Partner's interest in net income		802	620	1,109	738
Net income available to limited partners		85,109	67,754	117,686	80,615
Less dilutive impact of theoretical distribution of earnings	[1]	15,482	12,164	20,853	13,752
Limited Partner's interest in net income		$ 69,627	$ 55,590	$ 96,833	$ 66,863
Per unit data:
Basic and diluted net income available to limited partners		$ 2.46	$ 1.91	$ 3.4	$ 2.27
Less dilutive impact of theoretical distribution of earnings	[1]	0.45	0.35	0.6	0.39
Limited Partner's interest in net income	[2]	$ 2.01	$ 1.56	$ 2.8	$ 1.88
Weighted average number of Limited Partner units outstanding, Basic		34,569	35,549	34,578	35,571
Weighted average number of Limited Partner units outstanding, Diluted		34,569	35,549	34,578	35,571

[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.