Investments - Schedule of Fixed Maturities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Amortized Cost, net
Due in one year or less	$ 86,769
Due after one year through five years	857,913
Due after five years through ten years	2,034,083
Due after ten years through twenty years	8,712,181
Due after twenty years	7,684,013
Mortgage-backed and asset-backed securities	122,798
Fixed maturities, net of allowance for credit losses	19,497,757
Fair Value
Due in one year or less	86,518
Due after one year through five years	862,187
Due after five years through ten years	2,040,670
Due after ten years through twenty years	8,331,022
Due after twenty years	6,701,637
Mortgage-backed and asset-backed securities	122,319
Fixed maturities, fair value	$ 18,144,353	$ 17,870,206