Investments - Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Available for sale, Amortized Cost
Due in one year or less	$ 91,716
Due after one year through five years	245,541
Due after five years through ten years	54,940
Due after ten years	492,471
Agency mortgage-backed securities	607,080
Amortized Cost	1,491,748	$ 1,358,960
Available for sale, Estimated Fair Value
Due in one year or less	91,680
Due after one year through five years	234,843
Due after five years through ten years	52,433
Due after ten years	433,292
Agency mortgage-backed securities	580,196
Securities available-for-sale	1,392,444	1,366,006
Held to maturity, Amortized Cost
Due in one year or less	888
Due after one year through five years	18,315
Due after five years through ten years	150,791
Due after ten years	308,322
Agency mortgage-backed securities	63,281
Amortized Cost	541,597	430,295
Held to maturity, Estimated Fair Value
Due in one year or less	891
Due after one year through five years	17,994
Due after five years through ten years	144,456
Due after ten years	269,690
Agency mortgage-backed securities	60,311
Fair Value	$ 493,342	$ 434,672