Retirement Benefits - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Pension Benefit Cost (Credit)
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,990	$ 1,962	$ 6,319	$ 6,425
Interest cost	8,592	8,617	25,413	26,050
Expected return on plan assets	(10,772)	(10,211)	(32,314)	(30,587)
Amortization of prior service cost	22	29	68	82
Amortization of actuarial losses (gains)	2,232	2,845	5,937	8,729
Net periodic benefit cost (credit)	2,064	3,242	5,423	10,699
Other Postretirement Benefit Credit
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	12	22	38
Interest cost	151	181	483	559
Amortization of prior service cost	(5)	(237)	(15)	(705)
Amortization of actuarial losses (gains)	(102)	(141)	(270)	(464)
Net periodic benefit cost (credit)	$ 52	$ (185)	$ 220	$ (572)