Loans and Allowance for Credit Losses Present Loans, Net of Unearned Income and Their Related Allowance for Loan Losses, by Portfolio Segment (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012	Mar. 31, 2012		Dec. 31, 2011
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	$ 139,919			$ 159,190
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	80,122			97,306
Allowance for loan losses	220,041		223,903	256,496		256,471
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	12,114,733			11,658,592
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	262,555			301,412
Loans, net of unearned income	12,377,288		12,146,971	11,960,004
Real-estate commercial mortage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	40,920			50,619
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	23,065			31,033
Allowance for loan losses	63,985		62,928	81,652		85,112
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	4,646,355			4,523,691
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	83,575			110,737
Loans, net of unearned income	4,729,930			4,634,428
Commercial - industrial, financial, and agricultural
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	38,988			47,484
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	17,684			32,272
Allowance for loan losses	56,672		60,205	79,756		74,896
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	3,591,753			3,441,018
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	66,730			77,210
Loans, net of unearned income	3,658,483			3,518,228
Real-estate - home equity [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	14,947			9,549
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	8,754			3,534
Allowance for loan losses	23,701		22,776	13,083		12,841
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,675,577			1,595,522
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	13,869			6,358
Loans, net of unearned income	1,689,446			1,601,880
Real-estate - residential mortgage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	10,075			8,045
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	23,409			16,806
Allowance for loan losses	33,484		34,536	24,851		22,986
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,247,976			1,136,726
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	55,478			40,748
Loans, net of unearned income	1,303,454			1,177,474
Real-estate - construction
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	8,838			17,551
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	7,166			13,635
Allowance for loan losses	16,004		17,287	31,186		30,066
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	554,757			581,381
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	42,840			66,319
Loans, net of unearned income	597,597			647,700
Consumer
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	2,271			1,638
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	15			5
Allowance for loan losses	2,286		2,367	1,643		2,083
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	309,120			309,160
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	18			8
Loans, net of unearned income	309,138			309,168
Leasing and other and overdrafts [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	2,758			3,253
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	29			21
Allowance for loan losses	2,787		2,752	3,274		2,397
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	89,195			71,094
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	45			32
Loans, net of unearned income	89,240			71,126
Unallocated
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	21,122	[1]		21,051	[1]
Allowance for loan losses	$ 21,122	[1]	$ 21,052	$ 21,051	[1]	$ 26,090

[1] The unallocated allowance, which was approximately 10% and 8% of the total allowance for credit losses as of March 31, 2013 and March 31, 2012, respectively, was, in the opinion of management, reasonable and appropriate given that the estimates used in the allocation process are inherently imprecise.