Assets Acquired In FDIC-Assisted Acquisitions (Narrative) (Detail) (USD $)	1 Months Ended	9 Months Ended
	Jul. 06, 2012 Facility	Sep. 30, 2012	Sep. 30, 2011	Feb. 24, 2012 Facility	Dec. 31, 2011	Dec. 31, 2010
Number of branches operated by MBT	2
Customer deposits assumed by bank	$ 156,600,000
Customer deposits acquired	18,100,000
Cash and cash equivalents	16,700,000
Deposit secured loans	1,200,000
Cash payment, total	138,700,000
FDIC Shared-loss agreements		80.00%
FDIC Shared-loss agreements loss recoveries		80.00%
Number of branches				5
Estimated FDIC indemnification asset		198,440,000	239,719,000		242,394,000	177,187,000
Before-tax gain on acquisition		20,037,000	26,867,000
Total loans acquired		137,200,000
Total loans acquired, fair value		73,400,000
Accretable yield		10,200,000
Central Bank of Georgia (CBG)
Bid to acquire assets		33,900,000
Cash payment from FDIC to settle acquisition		31,900,000
Estimated FDIC indemnification asset		52,700,000
Before-tax gain on acquisition		20,000,000
Deferred tax liabilities recorded with respect to acquisitions		7,000,000
After-tax gain on acquisition		$ 13,000,000