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	96 Months Ended	97 Months Ended
		Nov. 30, 2021		Oct. 31, 2021		Sep. 30, 2021	Aug. 31, 2021		Jul. 31, 2021	Nov. 30, 2021		Sep. 30, 2021	Jun. 30, 2021		Mar. 31, 2021		Dec. 31, 2020		Sep. 30, 2021	Sep. 30, 2020	Jul. 31, 2020
Repurchase Plan
Capital Unit [Line Items]
Total Number of Units Purchased						337	223		25			585	568		538		2,591		4,282	17,697	14,400
Average Price Paid per Unit	[1]					$ 10.30	$ 10.68		$ 11.27			$ 10.49	$ 10.94		$ 9.67		$ 9.75		$ 10.00	$ 8.26
Maximum Number of Units that May Yet Be Purchased						2,848	3,185	[2]	3,408			2,848	3,433	[2]	4,001	[3]	4,539	[4],[5]	2,848	5,730
Repurchase Plan | Subsequent Event
Capital Unit [Line Items]
Total Number of Units Purchased		161		273						400
Average Price Paid per Unit		$ 10.99	[1]	$ 10.67	[1]					$ 10.79
Maximum Number of Units that May Yet Be Purchased		2,414	[6]	2,575						2,414	[6]
Publicly Announced Plans or Programs As Part of Repurchase Plan
Capital Unit [Line Items]
Total Number of Units Purchased						337	223		25			585	568		538		1,191		2,882	14,622
Publicly Announced Plans or Programs As Part of Repurchase Plan | Subsequent Event
Capital Unit [Line Items]
Total Number of Units Purchased		161		273

[1] Amounts include repurchase costs.

[2] On May 28, 2021, the Company purchased 0.3 million Common Units in a private transaction for aggregate consideration of approximately $2.8 million.  The purchase was made within the Company’s unit repurchase plan.

[3] On January 28, 2021, the Company purchased 0.1 million Common Units in a private transaction for aggregate consideration of approximately $1.3 million.  The purchase was made within the Company’s unit repurchase plan.

[4] On November 16, 2020, the Company purchased 1.4 million Common Units in a private transaction for aggregate consideration of approximately $13.8 million.  The purchase was made outside of the Company’s unit repurchase plan.

[5] On December 10, 2020, the Company purchased 0.4 million Common Units in a private transaction for aggregate consideration of approximately $4.2 million.  The purchase was made within the Company’s unit repurchase plan.

[6] Of the total available for repurchase, approximately 2.1 million are available for repurchase in open market   transactions and 0.3 million are available for repurchase in privately-negotiated transactions.