Equity and Noncontrolling Interests - Schedule of Redeemable Common Units (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Equity And Noncontrolling Interests [Line Items]
Redeemable common units, beginning of period	$ 6,121
Comprehensive income	60,610	55,963
Adjustment for ownership interest of redeemable common units	7	6
Stock-based compensation	1,934	1,764
Distributions to common unitholders	(41,313)	(31,665)
Adjustment to redemption value of redeemable common units	1,057	(134)
Redeemable common units, end of period	7,235
Redeemable Common Units [Member]
Equity And Noncontrolling Interests [Line Items]
Redeemable common units, beginning of period	6,121	7,159
Comprehensive income	147	141
Adjustment for ownership interest of redeemable common units	7	6
Stock-based compensation	5	4
Distributions to common unitholders	(102)	(83)
Adjustment to redemption value of redeemable common units	1,057	(134)
Redeemable common units, end of period	$ 7,235	$ 7,093