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, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ 0	$ (16,324)	$ (2,722)	$ 0	$ (19,046)
Pension Plans, Defined Benefiit
Defined Benefit Plan Disclosure [Line Items]
Service costs	248	292		502	553
Interest cost	2,503	2,916		5,079	6,031
Expected return on plan assets	(3,259)	(3,229)		(6,520)	(6,707)
Net amortization	363	851		733	1,732
Net periodic pension (benefit) cost	(145)	17,154		(206)	20,655
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		(16,324)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Interest cost	8	14		16	28
Net amortization	(55)	(52)		(110)	(104)
Net periodic pension (benefit) cost	$ (47)	$ (38)		$ (94)	$ (76)