Investment Securities (Summary of Amortized Cost and Fair Value of Held-To-Maturity Investment Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	$ 469,837	$ 316,413	$ 308,130
Investment securities held-to-maturity, Unrealized Gains	4,853	7,294	5,885
Investment securities held-to-maturity, Unrealized Losses	8,112	7,967	10,054
Total Held-to-maturity securities, Debt maturities, Fair Value	466,578	315,740	303,961
State and political subdivisions [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	469,337	305,913	297,630
Investment securities held-to-maturity, Unrealized Gains	4,853	7,294	5,885
Investment securities held-to-maturity, Unrealized Losses	7,912	4,557	6,329
Total Held-to-maturity securities, Debt maturities, Fair Value	466,278	308,650	297,186
Trust Preferred Securities [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	500	10,500	10,500
Investment securities held-to-maturity, Unrealized Gains	0	0	0
Investment securities held-to-maturity, Unrealized Losses	200	3,410	3,725
Total Held-to-maturity securities, Debt maturities, Fair Value	$ 300	$ 7,090	$ 6,775