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		Jun. 30, 2015		Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014		Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20		$ 119,922				$ 127,460
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35		47,563				64,225
Allowance for loan losses		167,485		$ 177,701	$ 184,144	191,685		$ 197,089	$ 202,780
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20		13,051,609				12,640,643
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35		192,621				198,868
Loans, net of unearned income		$ 13,244,230			13,111,716	$ 12,839,511
Percentage of unallocated allowance		6.00%				6.00%
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		$ 37,228				$ 33,388
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35		13,452				16,454
Allowance for loan losses		50,680		52,860	53,493	49,842		53,757	55,659
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20		5,172,333				5,067,400
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35		65,467				61,334
Loans, net of unearned income		5,237,800			5,197,155	5,128,734
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		38,090				36,603
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35		11,080				12,481
Allowance for loan losses		49,170		57,150	51,378	49,084		50,563	50,330
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20		3,764,999				3,558,788
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35		41,700				42,933
Loans, net of unearned income		3,806,699			3,725,567	3,601,721
Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20		15,838				22,234
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35		6,668				9,807
Allowance for loan losses		22,506		23,481	28,271	32,041		32,460	28,222
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20		1,676,410				1,715,953
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35		13,278				14,544
Loans, net of unearned income		1,689,688			1,736,688	1,730,497
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		8,763				11,450
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35		14,024				21,294
Allowance for loan losses		22,787		23,235	29,072	32,744		33,329	33,082
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20		1,315,908				1,309,739
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35		53,195				52,237
Loans, net of unearned income		1,369,103			1,377,068	1,361,976
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		5,430				7,163
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35		2,319				4,168
Allowance for loan losses		7,749		8,487	9,756	11,331		9,842	12,649
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20		712,975				606,221
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35		18,950				27,797
Loans, net of unearned income		731,925			690,601	634,018
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20		2,588				3,285
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35		20				21
Allowance for loan losses		2,608		2,527	3,015	3,306		3,324	3,260
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20		272,463				280,534
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35		31				23
Loans, net of unearned income		272,494			265,431	280,557
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		1,615				1,851
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35		0				0
Allowance for loan losses		1,615		1,653	1,799	1,851		2,011	3,370
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20		136,521				102,008
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35		0				0
Loans, net of unearned income		136,521			119,206	102,008
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	[1]	10,370				11,486
Allowance for loan losses		$ 10,370	[1]	$ 8,308	$ 7,360	$ 11,486	[1]	$ 11,803	$ 16,208

[1] The unallocated allowance, which was approximately 6% of the total allowance for credit losses as of both June 30, 2015 and June 30, 2014, was, in the opinion of management, reasonable and appropriate given that the estimates used in the allocation process are inherently imprecise.