Fair Value of Financial Instruments - Difference Between Fair Value and Principal Balance for Mortgage Loans Held for Sale Measured at Fair Value (Detail) (Mortgage Loans Held for Sale [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Mortgage Loans Held for Sale [Member]
Assets And Liabilities Carrying Value And Fair Value [Line Items]
Aggregate Fair Value of Mortgage Loans held for sale	$ 73,796	$ 94,759	$ 51,693
Aggregate Unpaid Principal Balance	70,905	90,418	49,959
Past due loans of 90 days or more	0	0	0
Nonaccrual loans	$ 0	$ 0	$ 0