Investment Securities, Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Amortized Cost [Abstract]
Within one year	$ 166,665
After one year through five years	16,515
After five years through ten years	1,239
After ten years	11,380
Amortized cost, excluding investment securities not due at a single maturity date	195,799
Investment securities not due at a single maturity date, mortgage-backed securities	288,549
Amortized cost	484,348	$ 499,639	$ 457,812
Fair/Book Value [Abstract]
Within one year	166,644
After one year through five years	16,760
After five years through ten years	1,241
After ten years	11,287
Fair/Book value, excluding investment securities not due at a single maturity date	195,932
Investment securities not due at a single maturity date, mortgage-backed securities	292,161
Fair/Book value	488,093	495,396	450,174
Book Value [Abstract]
Within one year	562
After one year through five years	3,513
After five years through ten years	24,440
After ten years	31,795
Book value, excluding investment securities not due at a single maturity date	60,310
Investment securities not due at a single maturity date, mortgage-backed securities	0
Book value	60,310	53,566	52,210
Fair Value [Abstract]
Within one year	563
After one year through five years	3,520
After five years through ten years	25,048
After ten years	32,024
Fair value, excluding investment securities not due at a single maturity date	61,155
Investment securities not due at a single maturity date, mortgage-backed securities	0
Fair value	$ 61,155	$ 53,738	$ 52,358