Securities (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Obligations of other U.S. Government agencies and corporations [Member]	Dec. 31, 2012 Obligations of other U.S. Government agencies and corporations [Member]	Sep. 30, 2012 Obligations of other U.S. Government agencies and corporations [Member]	Sep. 30, 2013 Obligations of states and political subdivisions [Member]	Dec. 31, 2012 Obligations of states and political subdivisions [Member]	Sep. 30, 2012 Obligations of states and political subdivisions [Member]
Amortized cost and fair value of securities held to maturity
Amortized Cost, Held to Maturity	$ 440,055	$ 317,766	$ 149,056	$ 90,045		$ 290,999	$ 227,721
Held to Maturity Securities, Gross Unrealized Gains Accumulated in Investments			13		116	8,352		16,860
Held to Maturity Securities, Gross Unrealized Loss Accumulated in Investments			(7,707)		(232)	(2,699)		(35)
Gross Unrealized Gains, Held to Maturity	8,365	16,976
Gross Unrealized Losses, Held to Maturity	(10,406)	(267)
Fair Value, Held to Maturity	$ 438,014	$ 334,475	$ 141,362	$ 89,929		$ 296,652	$ 244,546