Investments - Fixed-maturity Securities Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Available-for-sale Securities, Debt Maturities [Abstract]
Total available-for-sale fixed-maturity securities	$ 2,589,000	$ 2,495,456
Fixed Maturities
Available-for-sale Securities, Debt Maturities [Abstract]
Due in one year or less, amortized cost	180,451
Due after one year through five years, amortized cost	723,252
Due after five years through 10 years, amortized cost	819,372
Due after 10 years, amortized cost	325,402
Total fixed-maturity securities with single maturity dates, amortized cost	2,048,477
Mortgage and asset-backed securities, amortized cost	883,342
Available-for-sale debt securities, amortized cost basis	2,931,819	$ 2,801,415
Due in one year or less, fair value	178,021
Due after one year through five years, fair value	679,495
Due after five years through 10 years, fair value	700,703
Due after 10 years, fair value	263,364
Total fixed-maturity securities with single maturity dates, fair value	1,821,583
Mortgage and asset-backed securities, fair value	767,417
Total available-for-sale fixed-maturity securities	$ 2,589,000