Derivative Instruments and Hedging Activities - Losses Related to Interest Rate Derivatives Designated as Hedges of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
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	$ (38,899)	$ (39,014)
Amount of loss recognized in other comprehensive income	(8,911)	(6,298)
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	$ (1,629)	$ (1,648)