Pension And Other Postretirement Benefit Plans (Components Of Company's Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Settlement cost	$ 700
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5,990	$ 6,008	$ 5,177
Interest cost	10,747	10,810	10,801
Expected return on plan assets	(16,671)	(15,695)	(15,962)
Settlement cost	676	0	0
Net amortization and deferral	3,709	3,491	3,735
Net periodic benefit cost	4,451	4,614	3,751
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	199	222	229
Interest cost	1,306	1,371	1,471
Expected return on plan assets	(106)	(99)	(87)
Settlement cost	0	0	0
Net amortization and deferral	(647)	(710)	(620)
Net periodic benefit cost	$ 752	$ 784	$ 993