Commitments and Contingencies - Gains (Losses) Related to Interest Rate Derivatives Designated as Hedges of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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	$ (48,537)	$ (46,796)	$ (42,187)	$ (36,587)	$ (36,700)	$ (37,057)	$ (37,573)	$ (37,444)	$ (174,107)	$ (148,774)	$ (156,754)
Amount of gain (loss) recognized in other comprehensive income									1,005	(4,035)	(12,360)
Amounts Reclassified from Accumulated Other Comprehensive 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									$ (8,579)	$ (13,034)	$ (7,075)