Allowance for Credit Losses - Summary of Provision for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Banking And Thrift Interest [Abstract]
Provision for non-covered loans	$ 2,746	$ 7,429	$ 6,456	$ 12,803
Provision for covered loans	(110)		(2,276)
Total provision for loan losses	2,636	7,429	4,180	12,803
Provision for unfunded letters of credit	(84)	(24)	141	299
Total provision for credit losses	$ 2,552	$ 7,405	$ 4,321	$ 13,102