Investment Securities (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	$ 213,034	$ 183,339	$ 190,029
Investment securities held-to-maturity, Unrealized Gains	7,751	6,807	4,614
Investment securities held-to-maturity, Unrealized Losses	6,933	6,377	7,048
Investment securities held-to-maturity, Fair Value	213,852	183,769	187,595
State and political subdivisions [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	202,534	172,839	179,529
Investment securities held-to-maturity, Unrealized Gains	7,751	6,807	4,614
Investment securities held-to-maturity, Unrealized Losses	1,108	342	1,223
Investment securities held-to-maturity, Fair Value	209,177	179,304	182,920
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 Losses	5,825	6,035	5,825
Investment securities held-to-maturity, Fair Value	$ 4,675	$ 4,465	$ 4,675