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)