Loans and the Allowance for Credit Losses (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Summary of Commercial Loans by Risk Grade
Commercial loans	$ 2,115,734	$ 2,111,880
Commercial Real Estate Land and Construction [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	158,413	175,867
Commercial Real Estate Improved Property [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	1,536,632	1,509,698
Commercial and Industrial [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	420,689	426,315
Excellent - Minimal Risk [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	53,672	52,996
Excellent - Minimal Risk [Member] | Commercial Real Estate Land and Construction [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	443	625
Excellent - Minimal Risk [Member] | Commercial Real Estate Improved Property [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	382	448
Excellent - Minimal Risk [Member] | Commercial and Industrial [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	52,847	51,923
Good - Desirable Risk [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	821,663	819,586
Good - Desirable Risk [Member] | Commercial Real Estate Land and Construction [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	23,600	40,278
Good - Desirable Risk [Member] | Commercial Real Estate Improved Property [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	631,539	593,563
Good - Desirable Risk [Member] | Commercial and Industrial [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	166,524	185,745
Fair - Acceptable Risk [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	1,017,109	981,130
Fair - Acceptable Risk [Member] | Commercial Real Estate Land and Construction [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	105,245	97,077
Fair - Acceptable Risk [Member] | Commercial Real Estate Improved Property [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	740,431	727,594
Fair - Acceptable Risk [Member] | Commercial and Industrial [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	171,433	156,459
Criticized - Marginal [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	122,854	141,195
Criticized - Marginal [Member] | Commercial Real Estate Land and Construction [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	16,530	19,701
Criticized - Marginal [Member] | Commercial Real Estate Improved Property [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	89,427	107,433
Criticized - Marginal [Member] | Commercial and Industrial [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	16,897	14,061
Classified - Substandard [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	100,436	116,973
Classified - Substandard [Member] | Commercial Real Estate Land and Construction [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	12,595	18,186
Classified - Substandard [Member] | Commercial Real Estate Improved Property [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	74,853	80,660
Classified - Substandard [Member] | Commercial and Industrial [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	12,988	18,127
Classified - Doubtful [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	0	0
Classified - Doubtful [Member] | Commercial Real Estate Land and Construction [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	0	0
Classified - Doubtful [Member] | Commercial Real Estate Improved Property [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	0	0
Classified - Doubtful [Member] | Commercial and Industrial [Member]
Summary of Commercial Loans by Risk Grade
Commercial loans	$ 0	$ 0