Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	$ 5,076	$ 4,054	$ 14,773	$ 12,087
Interest cost on projected benefit obligations	2,102	3,709	6,227	11,081
Expected return on plan assets	(9,949)	(8,814)	(29,101)	(26,261)
Recognition of prior service cost	(1,837)	(1,679)	(5,335)	(5,033)
Recognition of actuarial losses/(gains)	6,583	5,569	19,170	16,672
Net periodic pension cost/(credit)	1,975	2,839	5,734	8,546
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	326	266	978	797
Interest cost on projected benefit obligations	889	1,146	2,667	3,438
Expected return on plan assets	(1,523)	(1,472)	(4,571)	(4,415)
Recognition of prior service cost	0	0	0	0
Recognition of actuarial losses/(gains)	643	593	1,933	1,780
Net periodic pension cost/(credit)	335	533	1,007	1,600
Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost, net	4,750	3,788	13,795	11,290
Interest cost on projected benefit obligations	1,208	2,547	3,541	7,595
Expected return on plan assets	(8,426)	(7,342)	(24,530)	(21,846)
Recognition of prior service cost	(1,819)	(1,679)	(5,279)	(5,033)
Recognition of actuarial losses/(gains)	5,947	5,149	17,258	15,410
Net periodic pension cost/(credit)	1,660	2,463	4,785	7,416
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	5	16	19	48
Expected return on plan assets	0	0	0	0
Recognition of prior service cost	(18)	0	(56)	0
Recognition of actuarial losses/(gains)	(7)	(173)	(21)	(518)
Net periodic pension cost/(credit)	$ (20)	$ (157)	$ (58)	$ (470)