Retirement Benefits - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,234	$ 3,270	$ 4,463	$ 6,570
Interest cost	8,724	5,140	17,433	10,299
Expected return on plan assets	(10,187)	(17,315)	(20,376)	(34,629)
Amortization of prior service cost	25	53	53	108
Amortization of actuarial losses (gains)	2,939	1,157	5,884	2,312
Net periodic benefit cost (credit)	3,735	(7,695)	7,457	(15,340)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	12	26	26	51
Interest cost	189	109	378	218
Amortization of prior service cost	(233)	(416)	(468)	(832)
Amortization of actuarial losses (gains)	(162)	(77)	(323)	(154)
Net periodic benefit cost (credit)	$ (194)	$ (358)	$ (387)	$ (717)