Investments - Schedule of Amortized Cost and Fair Value by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost
Due in one year or less	$ 23,768	$ 30,306
Due after one year through five years	227,073	149,378
Due after five years through ten years	55,470	26,621
Due after ten years	197,216	125,471
Asset-backed securities	36,151	37,975
Amortized cost	539,678	369,751
Fair Value
Due in one year or less	23,984	30,602
Due after one year through five years	228,476	153,406
Due after five years through ten years	55,445	27,479
Due after ten years	198,974	129,454
Asset-backed securities	34,242	36,192
Fair Value	$ 541,121	$ 377,133