Investments - Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value
Total	$ 1,026,438	$ 884,861
Fixed Maturities
Cost or Amortized Cost
Due in one year or less	93,973
Due after one year through five years	264,627
Due after five years through ten years	279,045
Due after ten years	16,228
Asset and mortgage backed securities	330,155
Cost or adjusted/amortized cost	$ 984,028	869,598
Percent of Total
Due in one year or less	9.50%
Due after one year through five years	26.90%
Due after five years through ten years	28.40%
Due after ten years	1.60%
Asset and mortgage backed securities	33.60%
Total	100.00%
Fair Value
Due in one year or less	$ 94,650
Due after one year through five years	276,916
Due after five years through ten years	295,069
Due after ten years	17,035
Asset and mortgage backed securities	342,768
Total	$ 1,026,438	$ 884,861
Percent of Total
Due in one year or less	9.20%
Due after one year through five years	27.00%
Due after five years through ten years	28.70%
Due after ten years	1.70%
Asset and mortgage backed securities	33.40%
Total	100.00%