Acquired SJB Assets and FDIC Loss Sharing Asset - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Oct. 16, 2009	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Business Combinations [Abstract]
Acquisition date		Oct. 16, 2009
After-tax gain included in earnings due to purchase method	$ 12,300,000
Remaining discount associated with SJB loans		7,100,000
Expected cash flows		4,600,000
Remaining average lives of respective pools loans		4 years
Remaining average lives of respective individual loans		3 months 18 days
FDIC loss sharing asset		299,000	4,764,000	18,489,000
Loss sharing agreement expiration date		Oct. 16, 2014
Allowance for SJB loans		0	0
Claims submitted for net losses on PCI loans		$ 122,000,000