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, 2014		Dec. 31, 2013	Mar. 31, 2013		Dec. 31, 2012
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	$ 133,188			$ 139,919
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	63,901			80,122
Allowance for loan losses	197,089		202,780	220,041		223,903
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	12,532,403			12,114,733
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	201,389			262,555
Loans, net of unearned income	12,733,792		12,782,220	12,377,288
Real-estate commercial mortage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	37,363			40,920
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	16,394			23,065
Allowance for loan losses	53,757		55,659	63,985		62,928
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	5,075,556			4,646,355
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	61,898			83,575
Loans, net of unearned income	5,137,454		5,101,922	4,729,930
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Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	36,859			38,988
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	13,704			17,684
Allowance for loan losses	50,563		50,330	56,672		60,205
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	3,528,857			3,591,753
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	45,273			66,730
Loans, net of unearned income	3,574,130		3,628,420	3,658,483
Home Equity [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	22,969			14,947
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	9,491			8,754
Allowance for loan losses	32,460		28,222	23,701		22,776
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,726,342			1,675,577
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	14,154			13,869
Loans, net of unearned income	1,740,496		1,764,197	1,689,446
Real-estate - residential mortgage [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	11,618			10,075
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	21,711			23,409
Allowance for loan losses	33,329		33,082	33,484		34,536
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	1,279,783			1,247,976
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	51,682			55,478
Loans, net of unearned income	1,331,465		1,337,380	1,303,454
Real-estate - construction
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	7,256			8,838
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	2,586			7,166
Allowance for loan losses	9,842		12,649	16,004		17,287
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	555,852			554,757
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	28,365			42,840
Loans, net of unearned income	584,217		573,672	597,597
Consumer
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	3,309			2,271
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	15			15
Allowance for loan losses	3,324		3,260	2,286		2,367
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	270,004			309,120
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	17			18
Loans, net of unearned income	270,021		283,124	309,138
Leasing and other and overdrafts [Member]
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	2,011			2,758
Allowance for loan losses evaluated for impairment under FASB ASC Section 310-10-35	0			29
Allowance for loan losses	2,011		3,370	2,787		2,752
Loans, net of unearned income, measured for impairment under FASB ASC Subtopic 450-20	96,009			89,195
Loans, net of unearned income, evaluated for impairment under FASB ASC Subtopic 310-10-35	0			45
Loans, net of unearned income	96,009		93,505	89,240
Unallocated
Allowance for loan losses measured for impairment under FASB ASC Subtopic 450-20	11,803	[1]		21,122	[1]
Allowance for loan losses	$ 11,803	[1]	$ 16,208	$ 21,122	[1]	$ 21,052

[1] The unallocated allowance, which was approximately 6% and 10% of the total allowance for credit losses as of March 31, 2014 and March 31, 2013, respectively, was, in the opinion of management, reasonable and appropriate given that the estimates used in the allocation process are inherently imprecise.