Employee Benefit Plans Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Components of Net Periodic Benefit Cost (Income) [Abstract]
Payment for pension benefits	$ 1,400
Minimum Expected Future Employer Pension Contributions, Remainder of Fiscal Year	10,000
Pension Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	2,846	$ 2,497
Interest cost	5,726	6,629
Expected return on plan assets	(6,545)	(6,362)
Amortization of prior service cost (credit)	0	1,652
Recognized actuarial loss (gain)	1,280	0
Net Periodic Benefit Cost (Credit)	3,307	4,416
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service cost	92	89
Interest cost	109	155
Expected return on plan assets	(247)	(218)
Amortization of prior service cost (credit)	(471)	(471)
Recognized actuarial loss (gain)	(18)	(24)
Net Periodic Benefit Cost (Credit)	$ (535)	$ (469)