Composition of Acquired Loans (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011	Jan. 27, 2012 Contractual Amount Tennessee Commerce Bank ("TCB")	Sep. 07, 2012 Contractual Amount First Commercial Bank("FCB")	Jan. 27, 2012 Fair Value Adjustments Tennessee Commerce Bank ("TCB")	Sep. 07, 2012 Fair Value Adjustments First Commercial Bank("FCB")	Jan. 27, 2012 Recast Adjustments Tennessee Commerce Bank ("TCB")	Jan. 27, 2012 Fair Value Tennessee Commerce Bank ("TCB")	Sep. 07, 2012 Fair Value First Commercial Bank("FCB")
Business Acquisition [Line Items]
Residential real estate	$ 750,000		$ 22,693,000	$ 48,409,000	$ (4,076,000)	$ (9,353,000)	$ 243,000	$ 18,860,000	$ 39,056,000
Commercial real estate	716,516,000	639,966,000	18,646,000	82,161,000	(6,971,000)	(12,688,000)	1,988,000	13,663,000	69,473,000
Real estate construction			14,877,000	14,918,000	(2,681,000)	(6,182,000)	(1,972,000)	10,224,000	8,736,000
Commercial	146,400,000	119,117,000	13,224,000	25,475,000	(6,939,000)	(15,983,000)	496,000	6,781,000	9,492,000
Home equity	251,072,000	280,235,000	6,220,000	404,000	(606,000)	(3,000)	24,000	5,638,000	401,000
Consumer:
Credit cards	8,570,000	8,580,000	608,000		(22,000)			586,000
Overdrafts	733,000	950,000	672,000	6,000	(621,000)			51,000	6,000
Other consumer	14,960,000	9,908,000	2,172,000	371,000	(750,000)	(5,000)	51,000	1,473,000	366,000
Total Loans	$ 2,642,357,000	$ 2,285,295,000	$ 79,112,000	$ 171,744,000	$ (22,666,000)	$ (44,214,000)	$ 830,000	$ 57,276,000	$ 127,530,000