Investment Securities, Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Amortized Cost [Abstract]
Within one year	$ 51,494
After one year through five years	5,153
After five years through ten years	601
After ten years	6,490
Amortized cost, excluding investment securities not due at a single maturity date	63,738
Investment securities not due at a single maturity date, mortgage-backed securities	286,529
Amortized cost	350,267	$ 789,175	$ 548,600
Fair Value [Abstract]
Within one year	51,587
After one year through five years	5,341
After five years through ten years	604
After ten years	6,512
Fair value, excluding investment securities not due at a single maturity date	64,044
Investment securities not due at a single maturity date, mortgage-backed securities	287,617
Fair value	351,661	807,732	569,407
Amortized Cost [Abstract]
Within one year	7,808
After one year through five years	5,804
After five years through ten years	21,182
After ten years	33,677
Book value, excluding investment securities not due at a single maturity date	68,471
Investment securities not due at a single maturity date, mortgage-backed securities	427,999
Amortized cost	496,470	68,933	69,036
Fair Value [Abstract]
Within one year	7,808
After one year through five years	5,840
After five years through ten years	21,937
After ten years	33,781
Fair value, excluding investment securities not due at a single maturity date	69,366
Investment securities not due at a single maturity date, mortgage-backed securities	420,819
Fair value	$ 490,185	$ 70,049	$ 70,194