Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Net of Tax
Balance at beginning and end of period	$ (330,851)	$ (456,799)
Other comprehensive income (loss)
Unrealized holding gains (losses) arising during the period, net of tax	114,917	(584,856)	$ (138,435)
Less: Reclassification adjustment for net gains (losses) on investments included in net income:
Net realized gains (losses) on disposals and non-credit related impairment losses	(10,852)	(7,880)	4,472
Net decrease (increase) in expected credit losses	0	0	725
Net unrealized gains (losses) on investments	125,769	(576,976)	(143,632)
Other adjustments to comprehensive income (loss), net	179	84	0
Other comprehensive income (loss), net of tax	125,948	(576,892)	(143,632)
Other Comprehensive Income (Loss)
Before Tax
Balance at beginning of period	(578,228)	152,016	333,829
Other comprehensive income (loss)
Unrealized holding gains (losses) arising during the period, before tax	145,465	(740,324)	(175,234)
Less: Reclassification adjustment for net gains (losses) on investments included in net income
Net realized gains (losses) on disposals and non-credit related impairment losses	(13,737)	(9,974)	5,661
Net decrease (increase) in expected credit losses			918
Net unrealized gains on investments	159,202	(730,350)	(181,813)
Other adjustments to comprehensive income, net	227	106
Other comprehensive income (loss)	159,429	(730,244)	(181,813)
Balance at end of period	(418,799)	(578,228)	152,016
Tax Effect
Balance at beginning of period	(121,429)	31,923	70,104
Other comprehensive income (loss)
Unrealized holding gains (losses) arising during the period, tax	30,548	(155,468)	(36,799)
Less: Reclassification adjustment for net gains (losses) on investments included in net income:
Net realized gains (losses) on disposals and non-credit related impairment losses	(2,885)	(2,094)	1,189
Net decrease (increase) in expected credit losses			193
Net unrealized gains on investments	33,433	(153,374)	(38,181)
Other adjustments to comprehensive income, net	48	22
Other comprehensive income (loss)	33,481	(153,352)	(38,181)
Balance at end of period	(87,948)	(121,429)	31,923
Net of Tax
Balance at beginning and end of period	(330,851)	(456,799)	120,093	$ 263,725
Other comprehensive income (loss)
Unrealized holding gains (losses) arising during the period, net of tax	114,917	(584,856)	(138,435)
Less: Reclassification adjustment for net gains (losses) on investments included in net income:
Net realized gains (losses) on disposals and non-credit related impairment losses	(10,852)	(7,880)	4,472
Net decrease (increase) in expected credit losses			725
Net unrealized gains (losses) on investments	125,769	(576,976)	(143,632)
Other adjustments to comprehensive income (loss), net	179	84
Other comprehensive income (loss), net of tax	$ 125,948	$ (576,892)	$ (143,632)