Investment Securities (Summary of Amortized Cost and Fair Value of Held-To-Maturity Investment Securities) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	$ 274,715	$ 229,977	$ 213,034
Investment securities held-to-maturity, Unrealized Gains	6,113	8,087	7,751
Investment securities held-to-maturity, Unrealized Losses	9,431	8,142	6,933
Investment securities held-to-maturity, Fair Value	271,397	229,922	213,852
State and political subdivisions [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	264,215	219,477	202,534
Investment securities held-to-maturity, Unrealized Gains	6,113	8,087	7,751
Investment securities held-to-maturity, Unrealized Losses	5,181	3,367	1,108
Investment securities held-to-maturity, Fair Value	265,147	224,197	209,177
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	4,250	4,775	5,825
Investment securities held-to-maturity, Fair Value	$ 6,250	$ 5,725	$ 4,675