Securities - Held-to-Maturity Securities Held by Company (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 139,216	$ 142,119
Gross Unrealized Gains	1,196	999
Gross Unrealized Losses	97	286
Fair Value	140,315	142,832
Obligations of U.S. Government sponsored entities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	131,707	132,098
Gross Unrealized Gains	1,103	804
Gross Unrealized Losses	90	283
Fair Value	132,720	132,619
Obligations of U.S. states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	7,509	10,021
Gross Unrealized Gains	93	195
Gross Unrealized Losses	7	3
Fair Value	$ 7,595	$ 10,213