Investment Securities (Summary of Amortized Cost and Fair Value of Held-To-Maturity Investment Securities) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	$ 308,130	$ 273,905	$ 274,715
Investment securities held-to-maturity, Unrealized Gains	5,885	5,462	6,113
Investment securities held-to-maturity, Unrealized Losses	10,054	11,096	9,431
Total Held-to-maturity securities, Debt maturities, Fair Value	303,961	268,271	271,397
State and political subdivisions [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	297,630	263,405	264,215
Investment securities held-to-maturity, Unrealized Gains	5,885	5,462	6,113
Investment securities held-to-maturity, Unrealized Losses	6,329	6,846	5,181
Total Held-to-maturity securities, Debt maturities, Fair Value	297,186	262,021	265,147
Trust Preferred Securities [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	10,500	10,500	10,500
Investment securities held-to-maturity, Unrealized Gains	0	0	0
Investment securities held-to-maturity, Unrealized Losses	3,725	4,250	4,250
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 6,775	$ 6,250	$ 6,250