Securities - (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Amortized cost and fair value of securities held to maturity
Amortized Cost	$ 439,070	$ 430,163
Gross Unrealized Gains	12,162	15,438
Gross Unrealized Losses	(3,572)	(3,113)
Fair Value	447,660	442,488
Obligations of other U.S. Government agencies and corporations
Amortized cost and fair value of securities held to maturity
Amortized Cost	125,596	125,081
Gross Unrealized Gains	19	10
Gross Unrealized Losses	(2,603)	(2,915)
Fair Value	123,012	122,176
Obligations of states and political subdivisions
Amortized cost and fair value of securities held to maturity
Amortized Cost	313,474	305,082
Gross Unrealized Gains	12,143	15,428
Gross Unrealized Losses	(969)	(198)
Fair Value	$ 324,648	$ 320,312