Equity and Noncontrolling Interests - Schedule of Redeemable Common Units (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Equity And Noncontrolling Interests [Line Items]
Redeemable common units, beginning of period	$ 7,086
Comprehensive income	38,760	$ 60,610
Stock-based compensation	2,625	1,934
Distributions to common unitholders	(45,858)	(41,313)
Adjustment to redemption value of redeemable common units	517	(1,057)
Redeemable common units, end of period	6,555
Redeemable Common Units [Member]
Equity And Noncontrolling Interests [Line Items]
Redeemable common units, beginning of period	7,086	6,121
Comprehensive income	81	147
Adjustment for ownership interest of redeemable common units	0	7
Stock-based compensation	6	5
Distributions to common unitholders	(101)	(102)
Adjustment to redemption value of redeemable common units	(517)	1,057
Redeemable common units, end of period	$ 6,555	$ 7,235