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, 2020	Jun. 30, 2019
Pension Plans, Defined Benefiit
Defined Benefit Plan Disclosure [Line Items]
Service costs	$ 261	$ 267
Interest cost	3,115	3,699
Expected return on plan assets	(3,479)	(3,973)
Net amortization	881	569
Net periodic pension (benefit) cost	3,500	562
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	(2,722)	0
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Interest cost	14	20
Net amortization	(52)	(40)
Net periodic pension (benefit) cost	$ (38)	$ (20)