Net Periodic Benefit Cost (Components of net periodic pension cost and net periodic postretirement benefit cost) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ (16,324)		$ (19,046)
Pension Plans, Defined Benefiit
Defined Benefit Plan Disclosure [Line Items]
Service costs	292	$ 248	553	$ 515
Interest cost	2,916	3,676	6,031	7,375
Expected return on plan assets	(3,229)	(3,972)	(6,707)	(7,945)
Net amortization	851	571	1,732	1,140
Net periodic pension (benefit) cost	17,154	523	20,655	1,085
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		0		0
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Interest cost	14	20	28	40
Net amortization	(52)	(40)	(104)	(80)
Net periodic pension (benefit) cost	$ (38)	$ (20)	$ (76)	$ (40)