Loans (Age Analysis of Past Due Loans, Segregated by Class of Loans) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Loans 30-89 Days Past Due	$ 62,367
Loans 90 or More Days Past Due	75,184
Total Past Due Loans	137,551
Current Loans	7,930,661
Total Loans	8,068,212	8,117,020	8,065,679
Accruing Loans 90 or More Days Past Due	12,992
Commercial And Industrial, Energy [Member]
Loans 30-89 Days Past Due	133
Loans 90 or More Days Past Due
Total Past Due Loans	133
Current Loans	802,199
Total Loans	802,332
Accruing Loans 90 or More Days Past Due
Commercial And Industrial, Other Commercial [Member]
Loans 30-89 Days Past Due	25,173
Loans 90 or More Days Past Due	40,229
Total Past Due Loans	65,402
Current Loans	2,974,416
Total Loans	3,039,818
Accruing Loans 90 or More Days Past Due	5,548
Commercial Real Estate, Buildings, Land And Other [Member]
Loans 30-89 Days Past Due	26,089
Loans 90 or More Days Past Due	25,826
Total Past Due Loans	51,915
Current Loans	2,572,052
Total Loans	2,623,967
Accruing Loans 90 or More Days Past Due	2,688
Commercial Real Estate, Construction [Member]
Loans 30-89 Days Past Due	2,581
Loans 90 or More Days Past Due	3,431
Total Past Due Loans	6,012
Current Loans	527,120
Total Loans	533,132
Accruing Loans 90 or More Days Past Due	1,511
Consumer Real Estate [Member]
Loans 30-89 Days Past Due	6,523
Loans 90 or More Days Past Due	5,481
Total Past Due Loans	12,004
Current Loans	761,065
Total Loans	773,069
Accruing Loans 90 or More Days Past Due	3,173
Consumer And Other [Member]
Loans 30-89 Days Past Due	1,868
Loans 90 or More Days Past Due	217
Total Past Due Loans	2,085
Current Loans	312,220
Total Loans	314,305
Accruing Loans 90 or More Days Past Due	72
Unearned Discounts [Member]
Loans 30-89 Days Past Due
Loans 90 or More Days Past Due
Total Past Due Loans
Current Loans	(18,411)
Total Loans	(18,411)
Accruing Loans 90 or More Days Past Due