Equity and Noncontrolling Interests - Schedule of Redeemable Common Units (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Equity And Noncontrolling Interests [Line Items]
Redeemable common units, beginning of period	$ 6,121
Comprehensive income	218,894	73,607
Conversion of redeemable common units for shares	(784)
Adjustment for ownership interest of redeemable common units	430	(42)
Stock-based compensation	2,950	2,715
Distributions to common unitholders	(63,097)	(49,550)
Adjustment to redemption value of redeemable common units	101	(725)
Redeemable common units, end of period	6,190
Redeemable Common Units [Member]
Equity And Noncontrolling Interests [Line Items]
Redeemable common units, beginning of period	6,121	7,159
Comprehensive income	465	185
Conversion of redeemable common units for shares	(784)
Adjustment for ownership interest of redeemable common units	430	(42)
Stock-based compensation	7	7
Distributions to common unitholders	(150)	(131)
Adjustment to redemption value of redeemable common units	101	(725)
Redeemable common units, end of period	$ 6,190	$ 6,453