Supplemental Information about Changes to Accumulated Other Comprehensive Income (Loss) - Schedule of Change in Balance by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 5,974,579	$ 5,305,520
Other comprehensive income (loss) before reclassifications, net of tax	70,646	61,433
Reclassifications, net of tax	7	(2,586)
Other comprehensive income (loss)	70,653	58,847
Ending balance	6,084,596	5,425,416
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,771,444)	(2,029,720)
Ending balance	(1,700,791)	(1,970,873)
Available for Sale Assets
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(969,982)	(1,319,618)
Other comprehensive income (loss) before reclassifications, net of tax	(253,842)	169,609
Reclassifications, net of tax	(1,240)	(2,639)
Other comprehensive income (loss)	(255,082)	166,970
Ending balance	(1,225,064)	(1,152,648)
Future Policy Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(821,628)	(709,042)
Other comprehensive income (loss) before reclassifications, net of tax	324,258	(110,089)
Reclassifications, net of tax	0	0
Other comprehensive income (loss)	324,258	(110,089)
Ending balance	(497,370)	(819,131)
Foreign Exchange
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(9,044)	(21,757)
Other comprehensive income (loss) before reclassifications, net of tax	230	1,913
Reclassifications, net of tax	0	0
Other comprehensive income (loss)	230	1,913
Ending balance	(8,814)	(19,844)
Pension Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	29,210	20,697
Other comprehensive income (loss) before reclassifications, net of tax	0	0
Reclassifications, net of tax	1,247	53
Other comprehensive income (loss)	1,247	53
Ending balance	$ 30,457	$ 20,750