Investments (Narrative) (Details) $ in Thousands	Sep. 30, 2024 USD ($) securities	Dec. 31, 2023 USD ($) securities
Schedule of Investments [Line Items]
Available-for-sale fixed maturity securities in unrealized loss position, number of positions | securities	1,079	1,386
Available-for-sale securities, estimated fair value	$ 8,500,420	$ 9,982,329
Available-for-sale securities, gross unrealized holding losses	$ (437,838)	$ (661,282)
Number of available-for-sale fixed maturity securities positions in a continuous unrealized loss position for one year or longer at period end | securities	1,032	1,131
Available-for-sale securities, estimated fair value, 12 months or longer	$ 7,875,442	$ 8,515,061
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(436,044)	(650,461)
Investments, available-for-sale, allowance for credit losses	$ 0	$ 0