Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Other comprehensive income (loss):
Other comprehensive income (loss)	$ (200,327)	$ 59,241	$ (246,182)	$ 160,924
Other comprehensive income (loss):
Other comprehensive (loss) income, tax effect	31,344	(9,000)	38,522	(22,365)
Net of Tax
Balance, beginning of period			5,756,727
Other comprehensive income (loss):
Total other comprehensive income (loss)	(168,983)	50,241	(207,660)	138,559
Balance, end of period	5,555,065	5,738,974	5,555,065	5,738,974
Accumulated Other Comprehensive Loss
Before Tax
AOCI before tax, beginning of period	(221,463)	(252,615)	(175,608)	(354,298)
Other comprehensive income (loss):
AOCI before tax, end of period	(421,790)	(193,374)	(421,790)	(193,374)
Tax Effect
AOCI tax effect, beginning of period	30,801	36,949	23,623	50,314
Other comprehensive income (loss):
AOCI tax effect, end of period	62,145	27,949	62,145	27,949
Net of Tax
Balance, beginning of period	(190,662)	(215,666)	(151,985)	(303,984)
Other comprehensive income (loss):
Total other comprehensive income (loss)	(168,983)	50,241	(207,660)	138,559
Balance, end of period	(359,645)	(165,425)	(359,645)	(165,425)
Accumulated Net Investment Gains (Losses) On Investments
Other comprehensive income (loss):
Unrealized holding gains (losses) arising during the period	(201,953)	58,816	(248,066)	160,189
Less: Reclassification adjustment for (gains) losses included in net income	1,626	425	1,884	735
Other comprehensive income (loss)	(200,327)	59,241	(246,182)	160,924
Other comprehensive income (loss):
Unrealized holding gains (losses) arising during the period	31,695	(8,916)	38,918	(22,220)
Less: Reclassification adjustment for gains (loss) included in net income	(351)	(84)	(396)	(145)
Other comprehensive (loss) income, tax effect	31,344	(9,000)	38,522	(22,365)
Other comprehensive income (loss):
Unrealized holding gains (losses) arising during the period	(170,258)	49,900	(209,148)	137,969
Less: Reclassification adjustment for (gains) losses included in net income	1,275	341	1,488	590
Total other comprehensive income (loss)	$ (168,983)	$ 50,241	$ (207,660)	$ 138,559

AOCI Attributable To Parent, Before Tax [Roll Forward]

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