Derivative Instruments and Hedging Activities - Losses Related to Interest Rate Derivatives Designated as Hedges of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 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	$ (39,577)	$ (39,745)	$ (78,476)	$ (78,759)
Amount of gain (loss) recognized in other comprehensive income	1,895	(8,368)	(7,016)	(14,666)
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
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	$ (1,699)	$ (1,664)	$ (3,328)	$ (3,312)