Investment Securities (Summary of Amortized Cost and Fair Value of Held-To-Maturity Investment Securities) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	$ 318,562	$ 273,905	$ 282,579
Investment securities held-to-maturity, Unrealized Gains	5,704	5,462	5,978
Investment securities held-to-maturity, Unrealized Losses	9,991	11,096	12,691
Total Held-to-maturity securities, Debt maturities, Fair Value	314,275	268,271	275,866
State and political subdivisions [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	308,062	263,405	272,079
Investment securities held-to-maturity, Unrealized Gains	5,704	5,462	5,978
Investment securities held-to-maturity, Unrealized Losses	6,476	6,846	8,441
Total Held-to-maturity securities, Debt maturities, Fair Value	307,290	262,021	269,616
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	3,515	4,250	4,250
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 6,985	$ 6,250	$ 6,250