Investment Securities - Schedule of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]
Amortized cost, Due in one year or less	$ 905	$ 9,290
Amortized cost, Due in one to five years	28,332	25,520
Amortized cost, Due in five to ten years	19,218	31,122
Amortized cost, Due in over ten years	67,016	62,909
Amortized cost, Total	115,471	128,841
Total debt securities, Amortized cost	541,028	579,715
Fair value, Due in one year or less	925	9,352
Fair value, Due in one to five years	28,878	26,340
Fair value, Due in five to ten years	19,588	32,248
Fair value, Due in over ten years	68,098	61,725
Fair value, Total	117,489	129,665
Total debt securities, Fair value	536,270	573,573
Mortgage-backed Securities - Residential
Schedule Of Available For Sale Securities [Line Items]
Total debt securities, Amortized cost	425,557	450,874
Total debt securities, Fair value	$ 418,781	$ 443,908