Investments in Securities - Investments classified by contractual maturity date (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Available-for-Sale - Amortized Cost
After three through four years	$ 245
After four through five years	952
After five through fifteen years	9,682
After fifteen years	48,262
Securities not due on a single maturity date	472,751
Available-for-sale securities, Amortized Cost, Total	531,892	$ 553,214
Available-for-Sale - Fair Value
After three through four years	245
After four through five years	981
After five through fifteen years	9,634
After fifteen years	47,277
Securities not due on a single maturity date	420,070
Available-for-sale securities, Fair Value, Total	478,207	490,592
Held-to-Maturity - Amortized Carrying Value
After five through fifteen years	3,247
After fifteen years	2,942
Securities not due on a single maturity date	188,834
Held-to-Maturity, Amortized Carrying Value, Total	195,023	202,495
Held-to-Maturity - Fair Value
After five through fifteen years	2,986
After fifteen years	2,721
Securities not due on a single maturity date	165,486
Held-to-maturity, Fair Value, Total	$ 171,193	$ 177,765