Other Comprehensive Income (Loss) - Pretax Components of Other Comprehensive Income (Loss) and Related Income Tax Benefit (Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Components of Other Comprehensive Income (Loss) [Abstract]
Net unrealized investment (losses) gains arising during the period	$ 179,174	$ (707,005)	$ (154,555)
Income tax (expense) benefit	(37,626)	148,471	32,456
Net of taxes	141,548	(558,534)	(122,099)
Net changes in benefit plan assets and obligations	29,978	(54,017)	31,613
Income tax benefit (expense)	(6,296)	11,343	(6,638)
Net of taxes	23,682	(42,674)	24,975
Total other comprehensive income (loss)	209,152	(761,022)	(122,942)
Total income tax benefit (expense)	(43,922)	159,814	25,818
Other comprehensive income (loss), net of tax	$ 165,230	$ (601,208)	$ (97,124)