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Pension And Other Postretirement Benefit Plans (Components Of Company's Net Periodic Benefit Cost) (Details) - USD ($)
$ in Thousands
12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2016
Pension Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 5,177 $ 5,382 $ 5,953
Interest cost 10,801 10,441 10,037
Expected return on plan assets (15,962) (15,154) (15,110)
Settlement gain 0 (912) 0
Net amortization and deferral 3,735 4,576 4,394
Net periodic benefit cost 3,751 4,333 5,274
Other Postretirement Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 229 247 286
Interest cost 1,471 1,535 1,539
Expected return on plan assets (87) (42) (58)
Settlement gain 0 0 0
Net amortization and deferral (620) (394) (431)
Net periodic benefit cost $ 993 $ 1,346 $ 1,336