Common Unit Repurchase and Retirement - Company's Repurchase Activities (Detail) - $ / shares shares in Thousands		1 Months Ended				3 Months Ended				72 Months Ended
		Jul. 30, 2019	Jun. 30, 2019	May 31, 2019	Apr. 30, 2019	Jun. 30, 2019	Mar. 31, 2019		Dec. 31, 2018	Sep. 30, 2018
Repurchase Plan
Capital Unit [Line Items]
Total Number of Units Purchased			111	552	222	885	2,187		599	7,937
Average Price Paid per Unit	[1]		$ 9.78	$ 9.67	$ 9.67	$ 9.68	$ 9.44		$ 9.57	$ 7.11
Maximum Number of Units that May Yet Be Purchased			1,688	1,799	2,351	1,688	2,573	[2]	4,760	5,359
Publicly Announced Plans or Programs As Part of Repurchase Plan
Capital Unit [Line Items]
Total Number of Units Purchased			111	552	222	885	2,187		599	5,493
Subsequent Event | Repurchase Plan
Capital Unit [Line Items]
Total Number of Units Purchased		136
Average Price Paid per Unit	[1]	$ 9.76
Maximum Number of Units that May Yet Be Purchased	[3]	1,552
Subsequent Event | Publicly Announced Plans or Programs As Part of Repurchase Plan
Capital Unit [Line Items]
Total Number of Units Purchased		136

[1] Amount includes repurchase costs.

[2] Second quarter of fiscal year 2019 common units repurchased include 1.2 million common units acquired in a private transaction.

[3] Of the total available for repurchase, approximately 0.3 million are available for repurchase in open market transactions and 1.3 million are available for repurchase in privately-negotiated transactions.