Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	$ 5,281	$ 4,854	$ 10,600	$ 9,697
Interest cost on projected benefit obligations	1,409	1,993	2,810	4,124
Expected return on plan assets	(10,398)	(9,541)	(20,863)	(19,152)
Recognition of prior service cost	(484)	(1,754)	(974)	(3,498)
Recognition of actuarial losses/(gains)	6,966	6,350	13,985	12,587
Net periodic pension cost/(credit)	2,774	1,902	5,558	3,758
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	374	326	748	652
Interest cost on projected benefit obligations	549	889	1,098	1,778
Expected return on plan assets	(1,494)	(1,524)	(2,988)	(3,048)
Recognition of prior service cost	0	0	0	0
Recognition of actuarial losses/(gains)	729	645	1,458	1,290
Net periodic pension cost/(credit)	158	336	316	672
Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	4,907	4,528	9,852	9,045
Interest cost on projected benefit obligations	858	1,097	1,708	2,332
Expected return on plan assets	(8,904)	(8,017)	(17,875)	(16,104)
Recognition of prior service cost	(465)	(1,735)	(936)	(3,460)
Recognition of actuarial losses/(gains)	6,246	5,712	12,545	11,311
Net periodic pension cost/(credit)	2,642	1,585	5,294	3,124
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description	27,900		27,900
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	0	0	0	0
Interest cost on projected benefit obligations	2	7	4	14
Expected return on plan assets	0	0	0	0
Recognition of prior service cost	(19)	(19)	(38)	(38)
Recognition of actuarial losses/(gains)	(9)	(7)	(18)	(14)
Net periodic pension cost/(credit)	(26)	$ (19)	(52)	$ (38)
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description	$ 200		$ 200