Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Unrealized investment (gains) losses on available for sale assets:
Realized (gains) losses	$ 11,799	$ 30,927
Net investment income	(282,578)	(257,105)
Other operating expense	93,214	84,171
Total before tax	(314,923)	(274,234)
Tax	60,706	50,624
Total after-tax	(254,217)	(223,610)
Reclassification out of Accumulated Other Comprehensive Income
Unrealized investment (gains) losses on available for sale assets:
Total after-tax	(1,814)	25,709
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	(228)	33,124
Net investment income	(2,184)	(534)
Total before tax	(2,412)	32,590
Tax	507	(6,844)
Total after-tax	(1,905)	25,746
Reclassification out of Accumulated Other Comprehensive Income | Pension adjustments:
Unrealized investment (gains) losses on available for sale assets:
Total before tax	118	(48)
Tax	(27)	11
Total after-tax	91	(37)
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
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)	$ (317)