Investments - Fixed-maturity Securities Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Available-for-sale Securities, Debt Maturities [Abstract]
Available-for-sale debt securities, at fair value	$ 2,705,131	$ 2,702,567
Fixed Maturities
Available-for-sale Securities, Debt Maturities [Abstract]
Due in one year or less, amortized cost	249,324
Due after one year through five years, amortized cost	773,970
Due after five years through 10 years, amortized cost	727,467
Due after 10 years, amortized cost	269,827
Total fixed-maturity securities with single maturity dates, amortized cost	2,020,588
Mortgage and asset-backed securities, amortized cost	768,929
Available-for-sale debt securities, amortized cost basis	2,789,517	2,621,388
Due in one year or less, fair value	251,212
Due after one year through five years, fair value	772,599
Due after five years through 10 years, fair value	690,427
Due after 10 years, fair value	255,090
Total fixed-maturity securities with single maturity dates, fair value	1,969,328
Mortgage and asset-backed securities, fair value	735,803
Available-for-sale debt securities, at fair value	$ 2,705,131	$ 2,702,567