Loans and the Allowance for Credit Losses (Details 3) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of commercial loans by risk grade
Commercial loans	$ 2,327,502	$ 2,336,370
Commercial Real Estate - Land and Construction [Member]
Summary of commercial loans by risk grade
Commercial loans	184,802	193,004
Commercial Real Estate - Improved Property [Member]
Summary of commercial loans by risk grade
Commercial loans	1,646,952	1,665,341
Commercial & Industrial [Member]
Summary of commercial loans by risk grade
Commercial loans	495,748	478,025
Excellent - minimal risk [Member]
Summary of commercial loans by risk grade
Commercial loans	67,173	65,044
Excellent - minimal risk [Member] | Commercial Real Estate - Land and Construction [Member]
Summary of commercial loans by risk grade
Commercial loans
Excellent - minimal risk [Member] | Commercial Real Estate - Improved Property [Member]
Summary of commercial loans by risk grade
Commercial loans	771	789
Excellent - minimal risk [Member] | Commercial & Industrial [Member]
Summary of commercial loans by risk grade
Commercial loans	66,402	64,255
Good - desirable risk [Member]
Summary of commercial loans by risk grade
Commercial loans	859,921	892,592
Good - desirable risk [Member] | Commercial Real Estate - Land and Construction [Member]
Summary of commercial loans by risk grade
Commercial loans	31,402	38,292
Good - desirable risk [Member] | Commercial Real Estate - Improved Property [Member]
Summary of commercial loans by risk grade
Commercial loans	676,809	701,447
Good - desirable risk [Member] | Commercial & Industrial [Member]
Summary of commercial loans by risk grade
Commercial loans	151,710	152,853
Fair - acceptable risk [Member]
Summary of commercial loans by risk grade
Commercial loans	1,232,274	1,205,997
Fair - acceptable risk [Member] | Commercial Real Estate - Land and Construction [Member]
Summary of commercial loans by risk grade
Commercial loans	135,898	136,643
Fair - acceptable risk [Member] | Commercial Real Estate - Improved Property [Member]
Summary of commercial loans by risk grade
Commercial loans	837,327	826,790
Fair - acceptable risk [Member] | Commercial & Industrial [Member]
Summary of commercial loans by risk grade
Commercial loans	259,049	242,564
Criticized - marginal [Member]
Summary of commercial loans by risk grade
Commercial loans	84,146	86,777
Criticized - marginal [Member] | Commercial Real Estate - Land and Construction [Member]
Summary of commercial loans by risk grade
Commercial loans	9,357	10,573
Criticized - marginal [Member] | Commercial Real Estate - Improved Property [Member]
Summary of commercial loans by risk grade
Commercial loans	65,968	66,906
Criticized - marginal [Member] | Commercial & Industrial [Member]
Summary of commercial loans by risk grade
Commercial loans	8,821	9,298
Classified - substandard [Member]
Summary of commercial loans by risk grade
Commercial loans	83,988	85,960
Classified - substandard [Member] | Commercial Real Estate - Land and Construction [Member]
Summary of commercial loans by risk grade
Commercial loans	8,145	7,496
Classified - substandard [Member] | Commercial Real Estate - Improved Property [Member]
Summary of commercial loans by risk grade
Commercial loans	66,077	69,409
Classified - substandard [Member] | Commercial & Industrial [Member]
Summary of commercial loans by risk grade
Commercial loans	9,766	9,055
Classified - doubtful [Member]
Summary of commercial loans by risk grade
Commercial loans
Classified - doubtful [Member] | Commercial Real Estate - Land and Construction [Member]
Summary of commercial loans by risk grade
Commercial loans
Classified - doubtful [Member] | Commercial Real Estate - Improved Property [Member]
Summary of commercial loans by risk grade
Commercial loans
Classified - doubtful [Member] | Commercial & Industrial [Member]
Summary of commercial loans by risk grade
Commercial loans