Securities (Held to maturity securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 256,355	$ 263,662
Gross Unrealized Gains	14,722	12,282
Gross Unrealized Losses	(691)	(1,145)
Estimated Fair Value	270,386	274,799
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	256,355	263,662
Gross Unrealized Gains	14,722	12,282
Gross Unrealized Losses	(691)	(1,145)
Estimated Fair Value	$ 270,386	$ 274,799