Retirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,270	$ 3,789	$ 6,570	$ 7,577
Interest cost	5,140	4,355	10,299	8,709
Expected return on plan assets	(17,315)	(19,850)	(34,629)	(39,698)
Amortization of prior service cost	53	58	108	116
Amortization of actuarial losses (gains)	1,157	3,028	2,312	6,054
Net periodic benefit credit	(7,695)	(8,620)	(15,340)	(17,242)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	26	28	51	56
Interest cost	109	95	218	190
Amortization of prior service cost	(416)	(457)	(832)	(913)
Amortization of actuarial losses (gains)	(77)	(47)	(154)	(95)
Net periodic benefit credit	$ (358)	$ (381)	$ (717)	$ (762)