Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Amortized cost and fair value of securities held to maturity
Amortized Cost	$ 482,410	$ 412,075
Gross Unrealized Gains	10,604	7,911
Gross Unrealized Losses	(8,234)	(11,410)
Fair Value	484,780	408,576
Obligations of other U.S. Government agencies and corporations
Amortized cost and fair value of securities held to maturity
Amortized Cost	185,056	125,061
Gross Unrealized Gains	10	14
Gross Unrealized Losses	(6,764)	(8,727)
Fair Value	178,302	116,348
Obligations of states and political subdivisions
Amortized cost and fair value of securities held to maturity
Amortized Cost	297,354	287,014
Gross Unrealized Gains	10,594	7,897
Gross Unrealized Losses	(1,470)	(2,683)
Fair Value	$ 306,478	$ 292,228