Company's Repurchase Activities (Detail) - $ / shares shares in Thousands		72 Months Ended
		Sep. 30, 2017		Dec. 31, 2017
Capital Unit [Line Items]
Company's common units authorized for repurchase				7,344
Plan III Common Units Repurchase Program
Capital Unit [Line Items]
Company's common units authorized for repurchase				4,894
Total Number of Units Purchased	[1],[2]	5,137
Average Price Paid per Unit	[1],[3]	$ 5.78
Maximum Number of Units that May Yet Be Purchased		2,207	[1]	2,207
Private Transaction
Capital Unit [Line Items]
Company's common units authorized for repurchase		2,450		2,450

[1] Includes 2.45 million common units acquired in a private transaction.

[2] Units were repurchased as part of a publicly announced program, except as noted in a private transaction.

[3] Amounts include repurchase costs.