Investment Securities HTM gross unreal losses (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAbstract
Unrealized losses on held to maturity securities, less than 12 months	$ (699)	$ (296)
Unrealized losses on held to maturity securities, 12 months or more	0	0
Total unrealized losses on held to maturity securities	(699)	(296)
Fair value of unrealized losses on held to maturity securities, less than 12 months	43,377	28,265
Fair value of unrealized losses on held to maturity securities, 12 months or more	0	0
Total fair value of unrealized losses on held to maturity securities	43,377	28,265
Obligations of state and political subdivisions (municipal securities) [Member]
HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAbstract
Unrealized losses on held to maturity securities, less than 12 months	(699)	(296)
Unrealized losses on held to maturity securities, 12 months or more	0	0
Total unrealized losses on held to maturity securities	(699)	(296)
Fair value of unrealized losses on held to maturity securities, less than 12 months	43,377	28,265
Fair value of unrealized losses on held to maturity securities, 12 months or more	0	0
Total fair value of unrealized losses on held to maturity securities	$ 43,377	$ 28,265
Number of held to maturity securities in a continuous unrealized loss position less than twelve months	90	56
Number of held to maturity securities in a continuous unrealized loss position for twelve months or more	0	0