Investment Securities (Summary of Amortized Cost and Fair Value of Held-to-Maturity Investment Securities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	$ 229,977	$ 183,339
Investment securities held-to-maturity, Unrealized Gains	8,087	6,807
Investment securities held-to-maturity, Unrealized Losses	8,142	6,377
Investment securities held-to-maturity, Fair Value	229,922	183,769
State and political subdivisions [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	219,477	172,839
Investment securities held-to-maturity, Unrealized Gains	8,087	6,807
Investment securities held-to-maturity, Unrealized Losses	3,367	342
Investment securities held-to-maturity, Fair Value	224,197	179,304
Trust preferred securities [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	10,500	10,500
Investment securities held-to-maturity, Unrealized Gains	0	0
Investment securities held-to-maturity, Unrealized Losses	4,775	6,035
Investment securities held-to-maturity, Fair Value	$ 5,725	$ 4,465