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, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Basic and Diluted Earnings Per Limited Partner:
Net income		$ 85,164	$ 58,408	$ 123,024	$ 86,163
Less General Partner’s interest in net income		681	409	977	601
Net income available to limited partners		84,483	57,999	122,047	85,562
Less dilutive impact of theoretical distribution of earnings	[1]	15,457	10,283	21,798	14,631
Limited Partner’s interest in net income		$ 69,026	$ 47,716	$ 100,249	$ 70,931
Per unit data:
Basic and diluted net income available to limited partners		$ 2.09	$ 1.25	$ 2.95	$ 1.83
Less dilutive impact of theoretical distribution of earnings	[1]	0.38	0.22	0.52	0.31
Limited Partner’s interest in net income	[2]	$ 1.71	$ 1.03	$ 2.43	$ 1.52
Weighted average number of Limited Partner units outstanding		40,382	46,244	41,324	46,760

[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 16 - Earnings Per Limited Partner Unit.