Investment Securities (Summary of Amortized Cost and Fair Value of Held-To-Maturity Investment Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	$ 278,099	$ 273,905	$ 257,749
Investment securities held-to-maturity, Unrealized Gains	5,331	5,462	10,002
Investment securities held-to-maturity, Unrealized Losses	11,023	11,096	6,346
Total Held-to-maturity securities, Debt maturities, Fair Value	272,407	268,271	261,405
State and political subdivisions [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	267,599	263,405	247,249
Investment securities held-to-maturity, Unrealized Gains	5,331	5,462	10,002
Investment securities held-to-maturity, Unrealized Losses	6,983	6,846	1,886
Total Held-to-maturity securities, Debt maturities, Fair Value	265,947	262,021	255,365
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	4,040	4,250	4,460
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 6,460	$ 6,250	$ 6,040