Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Unrealized investment (gains) losses on available for sale assets:
Realized (gains) losses	$ 45,843	$ 30,446	$ 76,770	$ 37,690
Net investment income	(261,244)	(244,712)	(518,349)	(489,606)
Other operating expense	86,033	89,658	170,204	174,010
Total before tax	(264,506)	(276,449)	(538,740)	(570,625)
Tax	49,246	52,476	99,870	109,168
Total after-tax	(215,260)	(223,973)	(438,870)	(461,457)
Reclassification out of Accumulated Other Comprehensive Income
Unrealized investment (gains) losses on available for sale assets:
Total after-tax	38,789	20,303	64,498	19,834
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gains (Losses) on Available for Sale Assets
Unrealized investment (gains) losses on available for sale assets:
Realized (gains) losses	50,347	22,422	83,471	17,485
Net investment income	(922)	(163)	(1,456)	744
Total before tax	49,425	22,259	82,015	18,229
Tax	(10,379)	(4,674)	(17,223)	(3,828)
Total after-tax	39,046	17,585	64,792	14,401
Reclassification out of Accumulated Other Comprehensive Income | Pension adjustments:
Unrealized investment (gains) losses on available for sale assets:
Total before tax	(323)	3,441	(371)	6,878
Tax	66	(723)	77	(1,445)
Total after-tax	(257)	2,718	(294)	5,433
Reclassification out of Accumulated Other Comprehensive Income | Amortization of prior service cost
Unrealized investment (gains) losses on available for sale assets:
Other operating expense	269	158	538	316
Reclassification out of Accumulated Other Comprehensive Income | Amortization of actuarial (gain) loss
Unrealized investment (gains) losses on available for sale assets:
Other operating expense	$ (592)	$ 3,283	$ (909)	$ 6,562