Investment Securities - Schedule of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized cost, Due in one year or less	$ 11,991	$ 905
Amortized cost, Due in one to five years	20,026	28,332
Amortized cost, Due in five to ten years	18,795	19,218
Amortized cost, Due in over ten years	80,261	67,016
Amortized cost, Total	131,073	115,471
Total debt securities, Amortized cost	625,672	541,028
Fair value, Due in one year or less	12,195	925
Fair value, Due in one to five years	20,083	28,878
Fair value, Due in five to ten years	18,769	19,588
Fair value, Due in over ten years	79,339	68,098
Fair value, Total	130,386	117,489
Available-for-sale debt securities, at fair value	608,360	536,270
Mortgage-backed Securities - Residential
Schedule Of Available For Sale Securities [Line Items]
Total debt securities, Amortized cost	494,599	425,557
Available-for-sale debt securities, at fair value	$ 477,974	$ 418,781