Accumulated Other Comprehensive Income (Loss) - Schedule Of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Before Tax
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	$ 183,113,000	$ (126,080,000)	$ 117,633,000	$ (94,777,000)
Net realized gains (losses) on disposals and non-credit related impairment losses	567,000	(2,794,000)	(6,188,000)	(13,180,000)
Net unrealized gains (losses) on investments	182,546,000	(123,286,000)	123,821,000	(81,597,000)
Other adjustments to comprehensive income (loss), net	0	0	(86,000)	227,000
Other comprehensive income (loss)	182,546,000	(123,286,000)	123,735,000	(81,370,000)
Tax Effect
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	38,454,000	(26,477,000)	24,703,000	(19,903,000)
Net realized gains (losses) on disposals and non-credit related impairment losses	119,000	(587,000)	(1,299,000)	(2,768,000)
Net unrealized gains (losses) on investments	38,335,000	(25,890,000)	26,002,000	(17,135,000)
Other adjustments to comprehensive income (loss), net	0	0	(18,000)	48,000
Other comprehensive income (loss)	38,335,000	(25,890,000)	25,984,000	(17,087,000)
Net of Tax
Balance at beginning of period			(330,851,000)
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	144,659,000	(99,603,000)	92,930,000	(74,874,000)
Net realized gains (losses) on disposals and non-credit related impairment losses	448,000	(2,207,000)	(4,889,000)	(10,412,000)
Net unrealized gains (losses) on investments	144,211,000	(97,396,000)	97,819,000	(64,462,000)
Other adjustments to other comprehensive income (loss)	0	0	(68,000)	179,000
Other comprehensive income (loss), net of tax	144,211,000	(97,396,000)	97,751,000	(64,283,000)
Balance at end of period	(233,100,000)		(233,100,000)
AOCI Attributable to Parent
Before Tax
Balance at beginning of period	(477,610,000)	(536,312,000)	(418,799,000)	(578,228,000)
Balance at end of period	(295,064,000)	(659,598,000)	(295,064,000)	(659,598,000)
Tax Effect
Balance at beginning of period	(100,299,000)	(112,626,000)	(87,948,000)	(121,429,000)
Balance at end of period	(61,964,000)	(138,516,000)	(61,964,000)	(138,516,000)
Net of Tax
Balance at beginning of period	(377,311,000)	(423,686,000)	(330,851,000)	(456,799,000)
Net unrealized gains (losses) on investments	144,211,000	(97,396,000)	97,819,000	(64,462,000)
Balance at end of period	$ (233,100,000)	$ (521,082,000)	$ (233,100,000)	$ (521,082,000)