Loans and Leases (Troubled Debt Restructurings By Class Segment) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012		Dec. 31, 2011
Financing Receivable Modifications [Line Items]
Total performing TDRs	$ 65,773				$ 67,775
TDRs [Member]
Financing Receivable Modifications [Line Items]
Total performing TDRs	65,773		72,081		67,775		72,852
Non-performing TDRs	25,808	[1],[2]	18,720	[1]	24,603	[2]
Total TDRs	91,581				92,378
Performing TDRs	72.00%		79.00%		73.00%
Non-performing TDRs	28.00%		21.00%		27.00%
Commercial, Financial, And Agricultural [Member] | TDRs [Member]
Financing Receivable Modifications [Line Items]
Total performing TDRs	14,863				8,744
Real Estate - Construction [Member] | TDRs [Member]
Financing Receivable Modifications [Line Items]
Total performing TDRs	937				940
Real Estate Secured - Residential [Member] | TDRs [Member]
Financing Receivable Modifications [Line Items]
Total performing TDRs	20,172				23,224
Real Estate Secured - Commercial [Member] | TDRs [Member]
Financing Receivable Modifications [Line Items]
Total performing TDRs	28,689				33,589
Consumer [Member] | TDRs [Member]
Financing Receivable Modifications [Line Items]
Total performing TDRs	$ 1,112				$ 1,278

[1] Included in Age Analysis of Past Due Financing Receivables.

[2] These loans are included in the 90 day past due and non-accrual categories.