Net Periodic Benefit Cost (Components of net periodic pension cost and net periodic postretirement benefit cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Pension Plans, Defined Benefiit
Defined Benefit Plan Disclosure [Line Items]
Service costs	$ 255	$ 235	$ 791	$ 1,491
Interest cost	3,864	3,982	11,629	12,438
Expected return on plan assets	(4,594)	(5,181)	(13,836)	(16,124)
Net amortization	572	696	1,750	2,325
Defined Benefit Plan, Accumulated Benefit Obligation, (Increase) Decrease for Settlement and Curtailment	0	5	0	5
Net periodic pension (benefit) cost	97	(263)	334	135
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Interest cost	28	35	85	105
Net amortization	(112)	0	(136)	0
Net periodic pension (benefit) cost	$ (84)	$ 35	$ (51)	$ 105