Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 1,353	$ 1,346
Interest cost	3,357	4,343
Expected return on plan assets	(5,648)	(6,100)
Prior service cost (benefit)	0	6
Net loss (gain)	2,093	941
Net periodic benefit cost	1,155	536
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	0
Estimated Future Employer Contributions in Current Fiscal Year	12,700
Estimated Future Employer Contributions in Next Fiscal Year	12,700
Other Postretirement Benefits Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	514	454
Interest cost	412	560
Expected return on plan assets	(45)	(57)
Prior service cost (benefit)	(137)	(99)
Net loss (gain)	5	0
Net periodic benefit cost	749	858
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	1,335
Estimated Future Employer Contributions in Current Fiscal Year	4,006
Estimated Future Employer Contributions in Next Fiscal Year	5,364
Supplemental Non-qualified Defined Benefit and Defined Contribution Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	(1,370)	1,285
Interest cost	275	324
Net loss (gain)	426	134
Net periodic benefit cost	(669)	$ 1,743
Payment for Pension and Other Postretirement Benefits [Abstract]
Contributions by Employer	355
Estimated Future Employer Contributions in Current Fiscal Year	1,065
Estimated Future Employer Contributions in Next Fiscal Year	$ 1,614