Common Unit Repurchase Plans and Retirement - Company's Repurchase Activities (Detail) - $ / shares shares in Thousands			1 Months Ended						2 Months Ended		3 Months Ended					12 Months Ended	131 Months Ended	144 Months Ended
		Jul. 31, 2025	Nov. 30, 2025	[3]	Oct. 31, 2025	[4]	Sep. 30, 2025	Aug. 31, 2025	Nov. 30, 2025		Sep. 30, 2025	Jun. 30, 2025	[1]	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2025	May 31, 2023	Sep. 30, 2024
Repurchase Plan
Capital Unit [Line Items]
Total Number of Units Purchased		144					157	172			473	817		6	13	1,309	20,500	26,438
Average Price Paid per Unit	[2]	$ 11.87					$ 11.73	$ 11.74			$ 11.78	$ 12.01		$ 11.24	$ 11.2	$ 11.92		$ 8.9
Maximum Number of Units that May Yet Be Purchased		1,272					943	1,100			943	1,416		1,533	1,539	943		1,552
Repurchase Plan | Subsequent Event
Capital Unit [Line Items]
Total Number of Units Purchased			67		234				300
Average Price Paid per Unit			$ 11.83	[2]	$ 11.87	[2]			$ 11.86
Maximum Number of Units that May Yet Be Purchased			642		709				642	[3]
Publicly Announced Plans or Programs As Part of Repurchase Plan
Capital Unit [Line Items]
Total Number of Units Purchased		144					157	172			473	117		6	13	609		21,550
Publicly Announced Plans or Programs As Part of Repurchase Plan | Subsequent Event
Capital Unit [Line Items]
Total Number of Units Purchased			67		234

[1] In May 2025, the Company purchased 700,000 Common Units in a private transaction for aggregate consideration of approximately $8.4 million. The purchase was made outside the Company’s unit repurchase plan.

[2] Amounts include repurchase costs.

[3] Of the total available for repurchase, approximately 0.5 million are available for repurchase in open market transactions and 0.1 million are available for repurchase in privately-negotiated transactions.

[4] In October 2025, the Company purchased 138,600 Common Units in a private transaction for aggregate consideration of approximately $1.6 million. The purchase was made within the Company’s unit repurchase plan.