Employee Benefit Plans (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Components of Net Period Benefit Cost
Service cost	$ 2,695,000	$ 2,120,000	$ 8,029,000	$ 6,311,000
Other cost:
Interest cost	4,970,000	5,584,000	14,910,000	16,799,000
Expected return on plan assets	(6,293,000)	(5,487,000)	(18,865,000)	(16,452,000)
Recognized net actuarial loss	1,460,000	824,000	3,416,000	2,599,000
Total other components of the net periodic benefit cost	137,000	921,000	(539,000)	2,946,000
Curtailment loss	1,753,000	0	1,753,000	0
Special termination benefits	5,258,000	0	5,258,000	0
Net periodic benefit cost	9,843,000	3,041,000	14,501,000	9,257,000
Contribution to defined benefit and other postretirement plans	0	$ 0	$ 0	$ 0
Increase (Decrease) in Obligation, Pension Benefits	33,700,000
Decrease of gain on plan remeasurement	$ 14,300,000
Minimum
Other cost:
Discount rate	2.48%
Maximum
Other cost:
Discount rate	2.81%