Retirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,300	$ 3,788
Interest cost	5,159	4,354
Expected return on plan assets	(17,314)	(19,848)
Amortization of prior service cost	55	58
Amortization of actuarial losses	1,155	3,026
Net periodic benefit credit	(7,645)	(8,622)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	25	28
Interest cost	109	95
Amortization of prior service cost	(416)	(456)
Amortization of actuarial losses	(77)	(48)
Net periodic benefit credit	$ (359)	$ (381)