Assets Acquired In FDIC-Assisted Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Before-gain on tax acquisition	$ 20,037,000	$ 26,867,000	$ 14,651,000
Estimated FDIC indemnification asset	159,724,000	242,394,000	177,187,000
Central Bank of Georgia (CBG) [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Assets acquisitions	20,000,000	26,900,000
Deferred tax liability recorded with respect to acquisition	7,000,000	9,400,000	5,200,000
After-tax gain on acquisition	13,000,000	17,500,000	9,600,000
Before-gain on tax acquisition			14,800,000
Fair value of the net assets acquired			956,000
Estimated FDIC indemnification asset	$ 52,700,000	$ 95,000,000