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
		Dec. 31, 2021	Dec. 31, 2020
Basic and Diluted Earnings Per Limited Partner:
Net income		$ 14,489	$ 37,860
Less General Partner’s interest in net income		122	296
Net income available to limited partners		14,367	37,564
Less dilutive impact of theoretical distribution of earnings	[1]	1,883	6,332
Limited Partner’s interest in net income		$ 12,484	$ 31,232
Per unit data:
Basic and diluted net income available to limited partners		$ 0.37	$ 0.89
Less dilutive impact of theoretical distribution of earnings	[1]	0.05	0.15
Limited Partner’s interest in net income		$ 0.32	$ 0.74
Weighted average number of Limited Partner units outstanding		38,789	42,246

[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.