Securities - Amortized Cost and Estimated Fair Value of Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 8,850	$ 5,980
Due after one year through five years	86,520	51,936
Due after five years through ten years	45,209	81,300
Due after ten years	0	0
Total held-to-maturity debt securities	140,579	139,216
Fair Value
Due in one year or less	8,832	5,979
Due after one year through five years	85,645	52,227
Due after five years through ten years	44,900	82,109
Due after ten years	0	0
Total held-to-maturity debt securities	$ 139,377	$ 140,315