Derivative Financial Instruments - Impact on Interest Expense of Interest Rate Agreements Accounted for as Cash Flow Hedges (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative [Line Items]
Total interest expense	$ (23,008)	$ (21,151)	$ (46,969)	$ (40,211)
Cash Flow Hedging | Interest Rate Contract
Derivative [Line Items]
Net interest expense on cash flow interest rate agreements	(1,475)	(1,490)	(2,959)	(2,978)
Realized income (expense) due to ineffective portion of hedges	0	0	0	0
Realized net losses reclassified from other comprehensive income	(26)	(39)	(57)	(99)
Total interest expense	$ (1,501)	$ (1,529)	$ (3,016)	$ (3,077)