Impact on Interest Expense of Interest Rate Agreements Accounted for as Cash Flow Hedges (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivative [Line Items]
Realized net losses reclassified from other comprehensive income	$ (69)	$ (1,000)	$ (157)	$ (2,000)
Total interest expense	(21,463)	(28,881)	(39,817)	(59,536)
Cash Flow Hedging | Interest Rate Contract
Derivative [Line Items]
Net interest expense on cash flow interest rate agreements	(1,470)	(1,437)	(2,934)	(2,953)
Realized income (expense) due to ineffective portion of hedges		5		(34)
Realized net losses reclassified from other comprehensive income	(69)	(1,098)	(157)	(2,134)
Total interest expense	$ (1,539)	$ (2,530)	$ (3,091)	$ (5,121)