Defined Benefit Pension and Other Postretirement Benefit Plans (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Mar. 31, 2019 USD ($)
Defined Benefit Plan Disclosure
Defined Benefit Plan, Number of Plans			12
Pension
Defined Benefit Plan Disclosure
Contribution by employer			$ 2,600
Net periodic benefit (income) costs
Net service cost	$ 1,245	$ 1,233	2,495	$ 2,466
Interest cost	462	478	924	956
Expected return on net assets	(482)	(531)	(955)	(1,062)
Amortization:
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	113	107	226	214
Prior service cost	21	23	42	46
Total net periodic benefit cost (credit)	1,359	1,310	2,732	2,620
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	(84,532)		(84,532)		$ (84,538)
Pension | Maximum
Defined Benefit Plan Disclosure
Estimated employer contribution in current fiscal year	5,100		5,100
Other Benefits
Net periodic benefit (income) costs
Net service cost	0	0	0	0
Interest cost	2	3	5	6
Expected return on net assets	0	0	0	0
Amortization:
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(37)	(39)	(74)	(77)
Prior service cost	0	0	0	0
Total net periodic benefit cost (credit)	(35)	$ (36)	(69)	$ (71)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	(295)		(295)		(312)
Prepaid Expenses and Other Current Assets [Member] | Pension
Defined Benefit Plan Disclosure
Assets for Plan Benefits, Defined Benefit Plan	(949)		(949)		(670)
Prepaid Expenses and Other Current Assets [Member] | Other Benefits
Defined Benefit Plan Disclosure
Assets for Plan Benefits, Defined Benefit Plan	0		0		0
Accrued Liabilities [Member] | Pension
Defined Benefit Plan Disclosure
Assets for Plan Benefits, Defined Benefit Plan	(2,758)		(2,758)		(2,753)
Accrued Liabilities [Member] | Other Benefits
Defined Benefit Plan Disclosure
Assets for Plan Benefits, Defined Benefit Plan	(50)		(50)		(50)
Other Noncurrent Liabilities [Member] | Pension
Defined Benefit Plan Disclosure
Assets for Plan Benefits, Defined Benefit Plan	(82,723)		(82,723)		(82,455)
Other Noncurrent Liabilities [Member] | Other Benefits
Defined Benefit Plan Disclosure
Assets for Plan Benefits, Defined Benefit Plan	$ (245)		$ (245)		$ (262)