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	Sep. 30, 2013		Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012		Jun. 30, 2012	Dec. 31, 2011
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	$ 145,050				$ 151,824
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	65,436				82,040
Allowance for loan losses	210,486		216,431	223,903	233,864		235,736	256,471
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	12,567,720				11,664,077
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	213,179				271,183
Loans, net of unearned income	12,780,899			12,146,971	11,935,260
Real-estate commercial mortage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	43,262				46,889
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	15,365				25,280
Allowance for loan losses	58,627		58,696	62,928	72,169		69,868	85,112
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	5,001,851				4,539,370
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	61,522				93,139
Loans, net of unearned income	5,063,373				4,632,509
Commercial - industrial, financial, and agricultural
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	38,025				44,169
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	13,870				23,705
Allowance for loan losses	51,895		57,557	60,205	67,874		71,931	74,896
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	3,593,038				3,430,724
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	52,232				77,122
Loans, net of unearned income	3,645,270				3,507,846
Real-estate - home equity [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	18,482				10,120
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	9,538				5,316
Allowance for loan losses	28,020		25,736	22,776	15,436		14,444	12,841
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,758,492				1,594,553
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	15,062				8,903
Loans, net of unearned income	1,773,554				1,603,456
Real-estate - residential mortgage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	11,494				8,306
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	22,263				20,550
Allowance for loan losses	33,757		32,684	34,536	28,856		26,711	22,986
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,277,200				1,165,504
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	50,269				48,818
Loans, net of unearned income	1,327,469				1,214,322
Real-estate - construction
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	8,648				14,957
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	4,383				7,171
Allowance for loan losses	13,031		14,471	17,287	22,128		25,559	30,066
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	543,268				554,185
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	34,074				43,173
Loans, net of unearned income	577,342				597,358
Consumer
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	2,911				1,858
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	17				5
Allowance for loan losses	2,928		2,497	2,367	1,863		1,816	2,083
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	296,122				301,710
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	20				7
Loans, net of unearned income	296,142				301,717
Leasing and other and overdrafts [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	2,982				2,980
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	0				13
Allowance for loan losses	2,982		2,925	2,752	2,993		3,243	2,397
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	97,749				78,031
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	0				21
Loans, net of unearned income	97,749				78,052
Unallocated
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	19,246	[1]			22,545	[1]
Allowance for loan losses	$ 19,246	[1]	$ 21,865	$ 21,052	$ 22,545	[1]	$ 22,164	$ 26,090

[1] The unallocated allowance, which was approximately 9% and 10% of the total allowance for credit losses as of September 30, 2013 and September 30, 2012, respectively, was, in the opinion of management, reasonable and appropriate given that the estimates used in the allocation process are inherently imprecise.