Details of Interest Income on Non accrual loans (Detail) - Non-Covered Loans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income that would have been recorded	$ 2,288	$ 3,997	$ 5,156
Interest income actually recorded	(1,574)	(3,017)	(2,721)
Interest income foregone	$ 714	$ 980	$ 2,435