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	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Assets And Liabilities Carrying Value And Fair Value [Line Items]
Aggregate Fair Value of Mortgage Loans held for sale	$ 108,829	$ 94,759	$ 81,491
Aggregate Unpaid Principal Balance	105,184	90,418	78,395
Past due loans of 90 days or more	0	0	0
Nonaccrual loans	$ 0	$ 0	$ 0