Company's Repurchase Activities (Detail) - $ / shares shares in Thousands		1 Months Ended				3 Months Ended			67 Months Ended
		Jul. 31, 2018	Jun. 30, 2018	May 31, 2018	Apr. 30, 2018	Jun. 30, 2018	Mar. 31, 2018		Jan. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
Plan III Common Units Repurchase Program
Capital Unit [Line Items]
Maximum Number of Units that May Yet Be Purchased			3,130	3,391	3,593	3,130	4,219	[1]		2,207	2,207
Total Number of Units Purchased			261	202	626	1,089	1,281		2,700
Average Price Paid per Unit	[2]		$ 9.56	$ 9.64	$ 9.71	$ 9.66	$ 9.38
Plan III Common Units Repurchase Program | Subsequent Event
Capital Unit [Line Items]
Maximum Number of Units that May Yet Be Purchased	[3],[4]	3,005
Total Number of Units Purchased	[4]	125
Average Price Paid per Unit	[2],[4]	$ 9.72
Publicly Announced Plans or Programs As Part of Plan III Common Units Repurchase Program
Capital Unit [Line Items]
Total Number of Units Purchased			261	202	626	1,089	1,281
Publicly Announced Plans or Programs As Part of Plan III Common Units Repurchase Program | Subsequent Event
Capital Unit [Line Items]
Total Number of Units Purchased	[4]	125

[1] In February 2018, the Board authorized an increase in the number of Common Units available for repurchase from 2.2 million to 5.5 million.

[2] Amount includes repurchase costs.

[3] Of the total available for repurchase, $0.5 million are available for repurchase in open market transactions and $2.5 million are available for repurchase in privately-negotiated transactions.

[4] See Note 14 - Subsequent Events.