Securities - (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Amortized cost and fair value of securities held to maturity
Amortized Cost	$ 476,752	$ 430,163
Gross Unrealized Gains	14,774	15,438
Gross Unrealized Losses	(1,293)	(3,113)
Fair Value	490,233	442,488
Obligations of other U.S. Government agencies and corporations
Amortized cost and fair value of securities held to maturity
Amortized Cost	120,602	125,081
Gross Unrealized Gains	32	10
Gross Unrealized Losses	(883)	(2,915)
Fair Value	119,751	122,176
Obligations of states and political subdivisions
Amortized cost and fair value of securities held to maturity
Amortized Cost	356,150	305,082
Gross Unrealized Gains	14,742	15,428
Gross Unrealized Losses	(410)	(198)
Fair Value	$ 370,482	$ 320,312