Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Other comprehensive income (loss):
Other comprehensive (losses) gain, before tax	$ (508,510)	$ (103,044)
Other comprehensive income (loss):
Other comprehensive (losses) gain, tax effect	75,013	15,477
Net of Tax
Stockholders equity, beginning of year	4,236,114	3,862,633
Other comprehensive income (loss):
Total other comprehensive (loss) income	(433,497)	(87,567)	$ 82,087
Stockholders equity, end of year	4,462,309	4,236,114	3,862,633
Income from other invested assets	28,676	56,386	(215)
Accumulated Other Comprehensive Income (Loss)
Before Tax
AOCI before tax, beginning of year	65,280	168,324
Other comprehensive income (loss):
AOCI before tax, end of year	(443,230)	65,280	168,324
Tax Effect
AOCI tax effect, beginning of year	(14,573)	(30,050)
Other comprehensive income (loss):
AOCI tax effect, end of year	60,440	(14,573)	(30,050)
Net of Tax
Stockholders equity, beginning of year	50,707	138,274	56,187
Other comprehensive income (loss):
Total other comprehensive (loss) income	(433,497)	(87,567)	82,087
Stockholders equity, end of year	(382,790)	50,707	$ 138,274
Accumulated Net Investment Gains (Losses) On Investments
Other comprehensive income (loss):
Unrealized holding (losses) gains arising during the year, before tax	(521,682)	(94,986)
Less: Reclassification adjustment for gains included in net income, before tax	13,172	(8,058)
Other comprehensive (losses) gain, before tax	(508,510)	(103,044)
Other comprehensive income (loss):
Unrealized holding (losses) gains arising during the year, tax effect	75,118	13,858
Less: Reclassification adjustment for gains included in net income, tax effect	(105)	1,619
Other comprehensive (losses) gain, tax effect	75,013	15,477
Other comprehensive income (loss):
Unrealized holding (losses) gains arising during the year, net of tax	(446,564)	(81,128)
Less: Reclassification adjustment for gains included in net income, net of tax	13,067	(6,439)
Total other comprehensive (loss) income	$ (433,497)	(87,567)
Accumulated Net Investment Gains (Losses) On Investments | Other Invested Assets
Other comprehensive income (loss):
Income from other invested assets		$ 7,600