Securities (Held to maturity securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 249,766	$ 253,550
Gross Unrealized Gains	9,699	12,460
Gross Unrealized Losses	(827)	(516)
Estimated Fair Value	258,638	265,494
Obligations of states and political subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	249,766	253,550
Gross Unrealized Gains	9,699	12,460
Gross Unrealized Losses	(827)	(516)
Estimated Fair Value	$ 258,638	$ 265,494