Reconciliation of Contractually Required and Carrying Amounts of Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Tennessee Commerce Bank ("TCB")	Dec. 31, 2012 Tennessee Commerce Bank ("TCB")	Jan. 27, 2012 Tennessee Commerce Bank ("TCB")	Mar. 31, 2013 First Commercial Bank("FCB")	Dec. 31, 2012 First Commercial Bank("FCB")	Sep. 07, 2012 First Commercial Bank("FCB")
Composition of Loan Acquired [Line Items]
Contractually-required principal	$ 157,560	$ 180,833	$ 36,191	$ 41,677	$ 79,000	$ 121,369	$ 139,156	$ 172,000
Non-accretable difference	(32,339)	(39,264)	(7,526)	(10,394)		(24,813)	(28,870)
Accretable difference	(2,300)	(2,953)	(312)	(319)		(1,988)	(2,634)
Carrying value of loans	$ 122,921	$ 138,616	$ 28,353	$ 30,964		$ 94,568	$ 107,652