Schedule of Location of Derivatives on Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Interest rate swaps - Asset Derivatives found in Interest rate hedge asset	$ 25,921
Forward purchase commitments - Asset Derivatives found in Other Assets		5,452
Futures contracts - Asset Derivatives found in Other Assets	5,587
Interest rate swaps - Asset Derivatives found in Interest rate hedge liability	157,869	243,945
Forward purchase commitments found in Account payable and other liabilities	$ 43,724