Loans (Loans) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and Industrial	$ 4,042,852	$ 3,723,244	$ 3,916,867
Total commercial real estate	3,034,884	3,212,694	3,020,827
Total consumer real estate	761,286	784,368	762,809
Total real estate	3,796,170	3,997,062	3,783,636
Total real estate percentage of total loans	46.70%	49.80%	47.30%
Total consumer and other	304,472	325,122	312,536
Unearned discounts	(16,781)	(20,348)	(17,910)
Unearned discounts percentage of total loans	(0.20%)	(0.30%)	(0.20%)
Total loans	8,126,713	8,025,080	7,995,129
Total loans percentage	100.00%	100.00%	100.00%
Commercial And Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and Industrial	4,042,852	3,723,244	3,916,867
Total commercial and industrial percentage of total loans	49.80%	46.40%	49.00%
Commercial And Industrial [Member] | Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and Industrial	3,709,450	3,393,769	3,553,989
Total commercial and industrial percentage of total loans	45.70%	42.30%	44.50%
Commercial And Industrial [Member] | Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and Industrial	193,162	194,692	193,412
Total commercial and industrial percentage of total loans	2.40%	2.40%	2.40%
Commercial And Industrial [Member] | Asset-Based [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and Industrial	140,240	134,783	169,466
Total commercial and industrial percentage of total loans	1.70%	1.70%	2.10%
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial mortgages	2,357,206	2,410,760	2,383,479
Commercial mortgages percentage of total loans	29.00%	30.00%	29.80%
Construction	493,600	574,637	434,870
Construction percentage of total loans	6.10%	7.20%	5.50%
Land	184,078	227,297	202,478
Land percentage of total loans	2.20%	2.80%	2.50%
Total commercial real estate	3,034,884	3,212,694	3,020,827
Total commercial real estate percentage of total loans	37.30%	40.00%	37.80%
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Home equity loans	288,961	274,952	282,244
Home equity loans percentage of total loans	3.60%	3.40%	3.50%
Home equity lines of credit	190,371	187,573	191,960
Home equity lines of credit percentage of total loans	2.40%	2.30%	2.40%
1-4 family residential mortgages	43,284	53,587	45,943
1-4 family residential mortgages percentage of total loans	0.50%	0.70%	0.60%
Construction	18,910	23,504	17,544
Construction percentage of total loans	0.20%	0.30%	0.20%
Other	219,760	244,752	225,118
Other percentage of total loans	2.70%	3.10%	2.80%
Total consumer real estate	761,286	784,368	762,809
Total consumer real estate percentage of total loans	9.40%	9.80%	9.50%
Total loans	761,286
Consumer And Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer installment	296,057	307,812	301,518
Consumer installment percentage of total loans	3.60%	3.90%	3.80%
Other	8,415	17,310	11,018
Other percentage of total loans	0.10%	0.20%	0.10%
Total consumer and other	304,472	325,122	312,536
Total consumer and other percentage of total loans	3.70%	4.10%	3.90%
Total loans	$ 304,472