Supplemental Information about Changes to Accumulated Other Comprehensive Income - Schedule of Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Unrealized investment (gains) losses on available for sale assets:
Realized (gains) losses	$ (85)	$ 11,799
Amortization of (discount) premium	(280,614)	(282,578)
Other operating expense	108,746	93,214
Total before tax	(316,081)	(314,923)
Tax	61,518	60,706
Total after-tax	(254,563)	(254,217)
Reclassification out of Accumulated Other Comprehensive Income
Unrealized investment (gains) losses on available for sale assets:
Total after-tax	(2,586)	(1,814)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized investment (gains) losses on available for sale assets:
Unrealized investment (gains) losses on available for sale assets:
Realized (gains) losses	(828)	(228)
Amortization of (discount) premium	(2,513)	(2,184)
Total before tax	(3,341)	(2,412)
Tax	702	507
Total after-tax	(2,639)	(1,905)
Reclassification out of Accumulated Other Comprehensive Income | Pension adjustments:
Unrealized investment (gains) losses on available for sale assets:
Total before tax	68	118
Tax	(15)	(27)
Total after-tax	53	91
Reclassification out of Accumulated Other Comprehensive Income | Amortization of prior service cost
Unrealized investment (gains) losses on available for sale assets:
Other operating expense	292	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	$ (224)	$ (151)