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, 2014		Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013		Jun. 30, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	$ 124,997				$ 145,050
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	64,480				65,436
Allowance for loan losses	189,477		191,685	202,780	210,486		216,431	223,903
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	12,836,973				12,567,720
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	193,432				213,179
Loans, net of unearned income	13,030,405			12,782,220	12,780,899
Percentage of unallocated allowance	4.00%				9.00%
Real-estate commercial mortage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	32,951				43,262
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	16,223				15,365
Allowance for loan losses	49,174		49,842	55,659	58,627		58,696	62,928
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	5,095,263				5,001,851
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	61,716				61,522
Loans, net of unearned income	5,156,979			5,101,922	5,063,373
Commercial - industrial, financial, and agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	39,098				38,025
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	11,942				13,870
Allowance for loan losses	51,040		49,084	50,330	51,895		57,557	60,205
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	3,655,162				3,593,038
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	36,100				52,232
Loans, net of unearned income	3,691,262			3,628,420	3,645,270
Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	21,666				18,482
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	9,625				9,538
Allowance for loan losses	31,291		32,041	28,222	28,020		25,736	22,776
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,719,049				1,758,492
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	13,987				15,062
Loans, net of unearned income	1,733,036			1,764,197	1,773,554
Real-estate - residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	11,503				11,494
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	21,502				22,263
Allowance for loan losses	33,005		32,744	33,082	33,757		32,684	34,536
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,319,333				1,277,200
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	52,700				50,269
Loans, net of unearned income	1,372,033			1,337,380	1,327,469
Real-estate - construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	6,009				8,648
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	5,167				4,383
Allowance for loan losses	11,176		11,331	12,649	13,031		14,471	17,287
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	658,822				543,268
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	28,906				34,074
Loans, net of unearned income	687,728			573,672	577,342
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	3,439				2,911
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	21				17
Allowance for loan losses	3,460		3,306	3,260	2,928		2,497	2,367
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	278,196				296,122
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	23				20
Loans, net of unearned income	278,219			283,124	296,142
Leasing and other and overdrafts [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	1,966				2,982
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	0				0
Allowance for loan losses	1,966		1,851	3,370	2,982		2,925	2,752
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	111,148				97,749
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	0				0
Loans, net of unearned income	111,148			93,505	97,749
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	8,365	[1]			19,246	[1]
Allowance for loan losses	$ 8,365	[1]	$ 11,486	$ 16,208	$ 19,246	[1]	$ 21,865	$ 21,052

[1] The unallocated allowance, which was approximately 4% and 9% of the total allowance for credit losses as of September 30, 2014 and September 30, 2013, respectively, was, in the opinion of management, reasonable and appropriate given that the estimates used in the allocation process are inherently imprecise.