Commitments and Contingencies - Gains (Losses) Related to Interest Rate Derivatives Designated as Hedges of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Amounts Related To Interest Rate Derivatives Included In Income Designated As Hedges Of Cash Flows [Line Items]
Amount of loss reclassified from accumulated other comprehensive loss to interest expense	$ (42,296)	$ (40,791)	$ (39,745)	$ (39,014)	$ (40,787)	$ (42,110)	$ (42,483)	$ (42,997)	$ (161,846)	$ (168,377)	$ (181,312)
Amount of gain (loss) recognized in other comprehensive income (loss)									(20,910)	4,255	(5,774)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Amounts Related To Interest Rate Derivatives Included In Income Designated As Hedges Of Cash Flows [Line Items]
Amount of loss reclassified from accumulated other comprehensive loss to interest expense									$ (6,663)	$ (6,898)	$ (6,478)