Unpaid Principal Balance of Mortgage Loans Held-for-Sale for Which Fair Value Option Elected by Type (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Mortgage loans held-for-sale at fair value	$ 10,672	$ 50,490
Government
Mortgage Loans on Real Estate [Line Items]
Mortgage loans held-for-sale at fair value	5,798	16,902
Conventional Mortgage Loan
Mortgage Loans on Real Estate [Line Items]
Mortgage loans held-for-sale at fair value	3,040	10,805
Jumbo
Mortgage Loans on Real Estate [Line Items]
Mortgage loans held-for-sale at fair value	1,757	20,514
Fair Value Adjustment
Mortgage Loans on Real Estate [Line Items]
Mortgage loans held-for-sale at fair value	$ 77	$ 2,269