Investments - Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Available for sale, Amortized Cost
Due in one year or less	$ 103,168
Due after one year through five years	367,426
Due after five years through ten years	99,210
Due after ten years	442,823
Agency mortgage-backed securities	717,605
Amortized Cost	1,730,232	$ 1,729,054
Available for sale, Estimated Fair Value
Due in one year or less	102,696
Due after one year through five years	340,209
Due after five years through ten years	88,070
Due after ten years	368,658
Agency mortgage-backed securities	650,742
Fair Value	1,550,375	1,535,807
Held to maturity, Amortized Cost
Due in one year or less	1,220
Due after one year through five years	60,531
Due after five years through ten years	187,374
Due after ten years	420,924
Agency mortgage-backed securities	54,768
Amortized Cost	724,817	710,650
Held to maturity, Estimated Fair Value
Due in one year or less	1,218
Due after one year through five years	55,811
Due after five years through ten years	176,372
Due after ten years	371,207
Agency mortgage-backed securities	48,536
Fair Value	$ 653,144	$ 628,517