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, 2019
Mar. 31, 2018
Mar. 31, 2017
Pension      
Defined Benefit Plan Disclosure [Line Items]      
Assets for Plan Benefits, Defined Benefit Plan $ 670 $ 0  
Amounts recognized in the Consolidated Balance Sheets      
Current liability (2,753) (7,000)  
Noncurrent liability (82,455) (83,182)  
Net Amount recognized, end of year (84,538) (90,182)  
Accumulated other comprehensive income (loss)      
Net actuarial loss (gain) 16,864 15,691  
Prior service cost 1,325 1,413  
Accumulated other comprehensive (income) loss 18,189 17,104  
Components of benefit costs (credit)      
Net service cost 4,716 4,585 $ 1,298
Interest cost 1,815 1,750 1,297
Expected return on plan assets (1) (2,037) (1,956) (346)
Amortization:      
Actuarial (gain) loss (2) 396 393 419
Prior service cost 87 87 82
Recurring activity 4,977 4,859 2,750
One time expense (income) 115 (71) (11)
Net periodic benefit cost (credit) 5,092 4,788 2,739
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 (50) (54)  
Noncurrent liability (262) (313)  
Net Amount recognized, end of year (312) (367)  
Accumulated other comprehensive income (loss)      
Net actuarial loss (gain) (793) (879)  
Prior service cost 0 0  
Accumulated other comprehensive (income) loss (793) (879)  
Components of benefit costs (credit)      
Net service cost 0 0 0
Interest cost 11 12 11
Expected return on plan assets (1) 0 0 0
Amortization:      
Actuarial (gain) loss (2) (167) (191) (207)
Prior service cost 0 0 0
Recurring activity (156) (179) (196)
One time expense (income) 0 0 0
Net periodic benefit cost (credit) $ (156) $ (179) $ (196)