Supplemental Information about Changes to Accumulated Other Comprehensive Income - Summary of Reclassifications (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Unrealized investment (gains) losses on available for sale assets:
Realized (gains) losses	$ 76,548	$ (68,633)	$ 3,737
Net investment income	(987,499)	(952,447)	(927,062)
Other operating expense	353,954	322,029	301,038
Total before tax	(906,311)	(912,390)	(896,684)
Tax	166,607	167,431	164,911
Total after-tax	(739,704)	(744,959)	(731,773)
Reclassification out of Accumulated Other Comprehensive Income
Unrealized investment (gains) losses on available for sale assets:
Total after-tax	36,443	(8,620)	39,058
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	32,165	(37,874)	26,345
Net investment income	212	6,164	6,464
Total before tax	32,377	(31,710)	32,809
Tax	(6,799)	6,659	(6,890)
Total after-tax	25,578	(25,051)	25,919
Reclassification out of Accumulated Other Comprehensive Income | Pension Adjustments
Unrealized investment (gains) losses on available for sale assets:
Total before tax	13,754	20,797	16,632
Tax	(2,889)	(4,366)	(3,493)
Total after-tax	10,865	16,431	13,139
Reclassification out of Accumulated Other Comprehensive Income | Amortization of prior service cost
Unrealized investment (gains) losses on available for sale assets:
Other operating expense	1,077	631	632
Reclassification out of Accumulated Other Comprehensive Income | Amortization of actuarial (gain) loss
Unrealized investment (gains) losses on available for sale assets:
Other operating expense	$ 12,677	$ 20,166	$ 16,000