Annual report pursuant to Section 13 and 15(d)

Pension and Other Post-retirement Benefit Plans - Amounts in Financial Statements (Details)

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Pension and Other Post-retirement Benefit Plans - Amounts in Financial Statements (Details) - USD ($)
$ in Thousands
12 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Mar. 31, 2018
Pension      
Defined Benefit Plan Disclosure [Line Items]      
Assets for Plan Benefits, Defined Benefit Plan $ 2,317 $ 670  
Amounts recognized in the Consolidated Balance Sheets      
Current liability (2,663) (2,753)  
Noncurrent liability (79,281) (82,455)  
Net liability recognized, end of year (79,627) (84,538)  
Accumulated other comprehensive income (loss)      
Net actuarial loss (gain) 16,673 16,864  
Prior service cost 2,034 1,325  
Accumulated other comprehensive (income) loss 18,707 18,189  
Components of benefit costs (credit)      
Net service cost 4,562 4,716 $ 4,585
Interest cost 1,830 1,815 1,750
Expected return on plan assets (1) (1,913) (2,037) (1,956)
Amortization:      
Actuarial (gain) loss (2) 444 396 393
Prior service cost 83 87 87
Recurring activity 5,006 4,977 4,859
One time expense (income) (3) 1,949 115 (71)
Net periodic benefit cost (credit) 6,955 5,092 4,788
Other Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Assets for Plan Benefits, Defined Benefit Plan 0 0  
Amounts recognized in the Consolidated Balance Sheets      
Current liability (47) (50)  
Noncurrent liability (231) (262)  
Net liability recognized, end of year (278) (312)  
Accumulated other comprehensive income (loss)      
Net actuarial loss (gain) (646) (793)  
Prior service cost 0 0  
Accumulated other comprehensive (income) loss (646) (793)  
Components of benefit costs (credit)      
Net service cost 0 0 0
Interest cost 9 11 12
Expected return on plan assets (1) 0 0 0
Amortization:      
Actuarial (gain) loss (2) (148) (167) (191)
Prior service cost 0 0 0
Recurring activity (139) (156) (179)
One time expense (income) (3) 0 0 0
Net periodic benefit cost (credit) $ (139) $ (156) $ (179)