Company's Repurchase Activities (Detail) - $ / shares shares in Thousands		1 Months Ended				3 Months Ended	67 Months Ended
		Apr. 30, 2018	Mar. 31, 2018	Feb. 28, 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			4,219	5,242	[1]	4,219	2,207	2,207	2,207
Total Number of Units Purchased			1,023	258		1,281	2,700
Average Price Paid per Unit	[2]		$ 9.36	$ 9.48		$ 9.38
Plan III Common Units Repurchase Program | Subsequent Event
Capital Unit [Line Items]
Maximum Number of Units that May Yet Be Purchased	[3]	3,593
Total Number of Units Purchased	[3]	626
Average Price Paid per Unit	[2],[3]	$ 9.71
Publicly Announced Plans or Programs As Part of Plan III Common Units Repurchase Program
Capital Unit [Line Items]
Total Number of Units Purchased			1,023	258		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	[3]	626

[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] See Note 14 - Subsequent Events