Equity and Noncontrolling Interests - Schedule of Redeemable Common Units (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Equity And Noncontrolling Interests [Line Items]
Redeemable common units, beginning of period	$ 7,086
Comprehensive income	57,689	$ 218,894
Conversion of redeemable common units for shares		784
Stock-based compensation	3,638	2,950
Distributions to common unitholders	(69,673)	(63,097)
Adjustment to redemption value of redeemable common units	(20)	(101)
Redeemable common units, end of period	7,028
Redeemable Common Units [Member]
Equity And Noncontrolling Interests [Line Items]
Redeemable common units, beginning of period	7,086	6,121
Comprehensive income	122	465
Conversion of redeemable common units for shares		(784)
Adjustment for ownership interest of redeemable common units	(54)	430
Stock-based compensation	8	7
Distributions to common unitholders	(154)	(150)
Adjustment to redemption value of redeemable common units	20	101
Redeemable common units, end of period	$ 7,028	$ 6,190