Allowance for Credit Losses - Summary of Provision for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Banking and Thrift, Interest [Abstract]
Provision for non-covered loans	$ 0	$ 4,280	$ 4,949	$ 10,736
Provision for covered loans	0		(5,671)	(2,276)
Total provision for loan losses	0	4,280	(722)	8,460
Provision for unfunded letters of credit	(423)	1,054	(1,374)	1,195
Total provision for credit losses	$ (423)	$ 5,334	$ (2,096)	$ 9,655