Retirement Benefits - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pension Benefit Cost (Credit)
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,165	$ 2,229
Interest cost	8,413	8,709
Expected return on plan assets	(10,771)	(10,189)
Amortization of prior service cost	23	28
Amortization of actuarial losses (gains)	1,852	2,945
Net periodic benefit cost (credit)	1,682	3,722
Other Postretirement Benefit Credit
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	14
Interest cost	165	189
Amortization of prior service cost	(5)	(235)
Amortization of actuarial losses (gains)	(84)	(161)
Net periodic benefit cost (credit)	$ 83	$ (193)