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, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Basic and Diluted Earnings Per Limited Partner:
Net income		$ 81,379	$ 85,164	$ 95,868	$ 123,024
Less General Partner’s interest in net income		697	681	819	977
Net income available to limited partners		80,682	84,483	95,049	122,047
Less dilutive impact of theoretical distribution of earnings	[1]	14,707	15,457	16,599	21,798
Limited Partner’s interest in net income		$ 65,975	$ 69,026	$ 78,450	$ 100,249
Per unit data:
Basic and diluted net income available to limited partners		$ 2.14	$ 2.09	$ 2.49	$ 2.95
Less dilutive impact of theoretical distribution of earnings	[1]	0.39	0.38	0.44	0.52
Limited Partner’s interest in net income		$ 1.75	$ 1.71	$ 2.05	$ 2.43
Weighted average number of Limited Partner units outstanding		37,634	40,382	38,218	41,324

[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.