Investment Securities (Details 1) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	$ 221,536	$ 183,339	$ 186,432
Investment securities held-to-maturity, Unrealized Gains	8,661	6,807	5,635
Investment securities held-to-maturity, Unrealized Losses	7,012	6,377	7,043
Investment securities held-to-maturity, Fair Value	223,185	183,769	185,024
State and political subdivisions [Member]
Held-to-maturity Securities
Investment securities held-to-maturity, Amortized Cost	211,036	172,839	175,932
Investment securities held-to-maturity, Unrealized Gains	8,661	6,807	5,635
Investment securities held-to-maturity, Unrealized Losses	1,712	342	1,008
Investment securities held-to-maturity, Fair Value	217,985	179,304	180,559
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	5,300	6,035	6,035
Investment securities held-to-maturity, Fair Value	$ 5,200	$ 4,465	$ 4,465