Allowance for Credit Losses - Summary of Provision for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Receivables [Abstract]
Provision for non-covered loans	$ 0	$ 0	$ 4,382	$ 4,949
Provision for covered loans	0	0	0	(5,671)
Total provision for loan losses	0	0	4,382	(722)
Provision for unfunded letters of credit	94	(423)	212	(1,374)
Total provision for credit losses	$ 94	$ (423)	$ 4,594	$ (2,096)