Schedule of Location of Derivatives on Income Statement (Detail) (Interest Rate Contract, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Interest Rate Contract
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative type for cash flow hedge	Interest Rate	Interest Rate
Amount of loss recognized in OCI on derivative (effective portion)	$ 5,907	$ 28,423
Location of loss reclassified from accumulated OCI into income (effective portion)	Interest Expense	Interest Expense
Amount of loss reclassified from accumulated OCI into income (effective portion)	29,929	27,811
Location of gain (loss)recognized in income on derivative (ineffective portion)	Interest Expense	Interest Expense
Amount of gain (loss) recognized in income on derivative (ineffective portion)	$ 116	$ 169