Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Unrealized investment (gains) losses on available for sale assets:
Realized (gains) losses	$ 12,589	$ 45,843	$ 24,388	$ 76,770
Net investment income	(285,636)	(261,244)	(568,214)	(518,349)
Other operating expense	99,108	86,033	192,322	170,204
Total before tax	(322,323)	(264,506)	(637,246)	(538,740)
Tax	63,968	49,246	124,674	99,870
Total after-tax	(258,355)	(215,260)	(512,572)	(438,870)
Reclassification out of Accumulated Other Comprehensive Income
Unrealized investment (gains) losses on available for sale assets:
Total after-tax	5,942	38,789	4,128	64,498
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	10,217	50,347	9,989	83,471
Net investment income	(2,817)	(922)	(5,001)	(1,456)
Total before tax	7,400	49,425	4,988	82,015
Tax	(1,554)	(10,379)	(1,047)	(17,223)
Total after-tax	5,846	39,046	3,941	64,792
Reclassification out of Accumulated Other Comprehensive Income | Pension adjustments:
Unrealized investment (gains) losses on available for sale assets:
Total before tax	118	(323)	236	(371)
Tax	(22)	66	(49)	77
Total after-tax	96	(257)	187	(294)
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	269	538	538
Reclassification out of Accumulated Other Comprehensive Income | Amortization of actuarial (gain) loss
Unrealized investment (gains) losses on available for sale assets:
Other operating expense	$ (151)	$ (592)	$ (302)	$ (909)