Securities - HTM Contractual Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
HTM, Amortized Cost, Rolling Maturities
Due in one year or less	$ 1,398
Due after one year through five years	25,735
Due after five years through ten years	4,914
Due after ten years	57,617
Total	89,664
Amortized cost	348,163	$ 355,849
HTM, Fair Value, Rolling Maturities
Due in one year or less	1,396
Due after one year through five years	24,447
Due after five years through ten years	4,769
Due after ten years	54,206
Total	84,818
Fair Value	332,388	349,939
Residential mortgage-backed Securities
HTM, Amortized Cost, Rolling Maturities
Mortgage-backed securities, collateralized mortgage obligations and commercial mortgage-backed securities	22,804
Amortized cost	22,804	16,130
HTM, Fair Value, Rolling Maturities
Mortgage-backed securities, collateralized mortgage obligations and commercial mortgage-backed securities	22,199
Fair Value	22,199	16,174
Collateralized mortgage obligations
HTM, Amortized Cost, Rolling Maturities
Mortgage-backed securities, collateralized mortgage obligations and commercial mortgage-backed securities	148,399
Amortized cost	148,399	173,928
HTM, Fair Value, Rolling Maturities
Mortgage-backed securities, collateralized mortgage obligations and commercial mortgage-backed securities	141,135
Fair Value	141,135	$ 169,978
Commercial mortgage-backed Securities
HTM, Amortized Cost, Rolling Maturities
Mortgage-backed securities, collateralized mortgage obligations and commercial mortgage-backed securities	87,296
HTM, Fair Value, Rolling Maturities
Mortgage-backed securities, collateralized mortgage obligations and commercial mortgage-backed securities	$ 84,236