Investments - Amortized Cost and Estimated Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less, Amortized Cost	$ 37,045
Due after one year through five years, Amortized Cost	271,840
Due after five years though ten years, Amortized Cost	349,628
Due after ten years through twenty years, Amortized Cost	47,743
Due after twenty years, Amortized Cost	1,269
Asset-backed securities, Amortized Cost	458,067
Totals, Amortized Cost	1,165,592	$ 1,187,857
Estimated Fair Value
Due in one year or less, Fair Value	36,894
Due after one year through five years, Fair Value	268,631
Due after five years through ten years, Fair Value	338,371
Due after ten years through twenty years, Fair Value	46,712
Due after twenty years, Fair Value	1,630
Asset-backed securities, Fair Value	443,830
Totals, Fair Value	$ 1,136,068	$ 1,218,279