Investment Securities - Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less	$ 38,547
Due after one year through five years	193,191
Due after five years through ten years	272,408
Due after ten years	481,395
Amortized Cost	985,541
Fair Value
Due in one year or less	38,478
Due after one year through five years	192,556
Due after five years through ten years	268,779
Due after ten years	476,282
Fair Value	$ 976,095	$ 810,530