Net Periodic Benefit Cost (Components of net periodic pension cost and net periodic postretirement benefit cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ 0	$ (2,722)
Pension Plans, Defined Benefiit
Defined Benefit Plan Disclosure [Line Items]
Service costs	254		$ 261
Interest cost	2,576		3,115
Expected return on plan assets	(3,261)		(3,479)
Net amortization	370		881
Net periodic pension (benefit) cost	(61)		3,500
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement			(2,722)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Interest cost	8		14
Net amortization	(55)		(52)
Net periodic pension (benefit) cost	$ (47)		$ (38)