Retirement Benefits - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pension Benefit Cost (Credit)
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,164	$ 2,234	$ 4,329	$ 4,463
Interest cost	8,408	8,724	16,821	17,433
Expected return on plan assets	(10,771)	(10,187)	(21,542)	(20,376)
Amortization of prior service cost	23	25	46	53
Amortization of actuarial losses (gains)	1,853	2,939	3,705	5,884
Net periodic benefit cost (credit)	1,677	3,735	3,359	7,457
Other Postretirement Benefit Credit
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	12	14	26
Interest cost	167	189	332	378
Amortization of prior service cost	(5)	(233)	(10)	(468)
Amortization of actuarial losses (gains)	(84)	(162)	(168)	(323)
Net periodic benefit cost (credit)	$ 85	$ (194)	$ 168	$ (387)