Accumulated Other Comprehensive Income (Loss) - Rollforward of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Before Tax
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	$ (223,279)	$ (29,613)	$ (797,908)	$ (134,539)
Net realized gains (losses) on disposals and non-credit related impairment losses	(4,153)	4,099	(10,071)	5,684
Net decrease (increase) in expected credit losses		0		918
Net unrealized gains (losses) on investments	(219,126)	(33,712)	(787,837)	(141,141)
Other adjustments to comprehensive income (loss), net	0		106
Other comprehensive income (loss)	(219,126)	(33,712)	(787,731)	(141,141)
Tax Effect
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	(46,888)	(6,219)	(167,560)	(28,253)
Net realized gains (losses) on disposals and non-credit related impairment losses	(872)	861	(2,115)	1,194
Net decrease (increase) in expected credit losses		0		193
Net unrealized gains (losses) on investments	(46,016)	(7,080)	(165,445)	(29,640)
Other adjustments to comprehensive income (loss), net	0		22
Other comprehensive income (loss)	(46,016)	(7,080)	(165,423)	(29,640)
Net of Tax
Balance at beginning and end of the period	(502,215)		(502,215)			$ 120,093
Unrealized holding gains (losses) on investments arising during the period for which an allowance for expected credit losses has not been recognized	(176,391)	(23,394)	(630,348)	(106,286)
Net realized gains (losses) on disposals and non-credit related impairment losses	(3,281)	3,238	(7,956)	4,490
Net decrease (increase) in expected credit losses	0	0	0	725
Net unrealized gains (losses) on investments	(173,110)	(26,632)	(622,392)	(111,501)
Other adjustments to other comprehensive income (loss)	0	0	84	0
Other comprehensive income (loss), net of tax	(173,110)	(26,632)	(622,308)	(111,501)
AOCI Attributable to Parent
Before Tax
Balance at beginning of period	(416,589)	226,400	152,016	333,829
Balance at end of period	(635,715)	192,688	(635,715)	192,688
Tax Effect
Balance at beginning of period	(87,484)	47,544	31,923	70,104
AOCI Tax, Balance at end of period	(133,500)	40,464	(133,500)	40,464
Net of Tax
Balance at beginning and end of the period	(502,215)	152,224	(502,215)	152,224	$ (329,105)	$ 120,093	$ 178,856	$ 263,725
Net unrealized gains (losses) on investments	$ (173,110)	$ (26,632)	$ (622,392)	$ (111,501)