Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	$ 4,854	$ 4,065	$ 9,697	$ 8,032
Interest cost on projected benefit obligations	1,993	3,682	4,124	7,387
Expected return on plan assets	(9,541)	(8,690)	(19,152)	(17,463)
Recognition of prior service cost	(1,754)	(1,637)	(3,498)	(3,339)
Recognition of actuarial losses/(gains)	6,350	5,482	12,587	11,088
Net periodic pension cost/(credit)	1,902	2,902	3,758	5,705
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	326	266	652	532
Interest cost on projected benefit obligations	889	1,146	1,778	2,292
Expected return on plan assets	(1,524)	(1,472)	(3,048)	(2,944)
Recognition of prior service cost	0	0	0	0
Recognition of actuarial losses/(gains)	645	593	1,290	1,187
Net periodic pension cost/(credit)	336	533	672	1,067
Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	4,528	3,799	9,045	7,500
Interest cost on projected benefit obligations	1,097	2,520	2,332	5,063
Expected return on plan assets	(8,017)	(7,218)	(16,104)	(14,519)
Recognition of prior service cost	(1,735)	(1,637)	(3,460)	(3,339)
Recognition of actuarial losses/(gains)	5,712	5,062	11,311	10,247
Net periodic pension cost/(credit)	1,585	2,526	3,124	4,952
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description	25,600		25,600
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	0	0	0	0
Interest cost on projected benefit obligations	7	16	14	32
Expected return on plan assets	0	0	0	0
Recognition of prior service cost	(19)	0	(38)	0
Recognition of actuarial losses/(gains)	(7)	(173)	(14)	(346)
Net periodic pension cost/(credit)	$ (19)	$ (157)	$ (38)	$ (314)