Differences Between Fair Value Carrying Amount of Loans Held for Sale Measured at Fair Value and Aggregate Unpaid Principal Amount Entitled to Receive at Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Carrying Amount, Total loans	$ 138,301	$ 41,990
Aggregate Unpaid Principal, Total loans	130,622
Fair Value Carrying Amount Less Aggregate Unpaid Principal, Total loans	$ 7,679