Leases (Details) - USD ($) $ in Millions		3 Months Ended	6 Months Ended	12 Months Ended
		Sep. 30, 2019	Sep. 30, 2019	Mar. 31, 2019	Mar. 31, 2018
Lease Assets [Abstract]
Right-of-use assets		$ 64.7	$ 64.7	$ 61.3
Finance lease ROU assets, Property, plant and equipment - net	[1]	8.6	8.6
Lease Liabilities [Abstract]
Operating lease liabilities, Other current liabilities		10.1	10.1
Operating lease liabilities, Other noncurrent liabilities		53.1	53.1
Finance lease liabilities, Long-term debt - current portion		0.3	0.3
Finance lease liabilities, Long-term debt		3.5	3.5
Accumulated amortization		1.5	1.5
Components of Lease Expense [Abstract]
Operating lease expense	[2]	5.2	10.4
Finance lease expense [Abstract]
Depreciation of ROU assets		0.1	0.2
Interest on lease liabilities		0.1	0.1
Total lease expense		5.4	10.7
Short-term lease expense		1.0	1.9
Cash paid for amounts included in measurement of lease liabilities [Abstract]
Operating cash flows for operating leases		4.2	7.9
Financing cash flows for finance leases		0.1	0.2
ROU assets obtained in exchange for lease liabilities [Abstract]
Operating leases		5.1	5.4
Finance leases		$ 0.1	$ 0.1
Weighted-average remaining lease term [Abstract]
Operating leases		9 years 3 months 18 days	9 years 3 months 18 days
Finance leases		9 years 3 months 18 days	9 years 3 months 18 days
Weighted-average discount rate [Abstract]
Operating leases		3.50%	3.50%
Finance leases		4.80%	4.80%
Maturity of Operating Lease Liabilities [Abstract]
Remainder of fiscal 2020		$ 6.0	$ 6.0
2021		12.1	12.1
2022		10.6	10.6
2023		8.6	8.6
2024		6.1	6.1
2025 and beyond		31.1	31.1
Total lease payments		74.5	74.5
Less: Interest		(11.3)	(11.3)
Present value of lease liabilities		63.2	63.2
Maturities of Finance Lease Liabilities [Abstract]
Remainder of fiscal 2020		0.3	0.3
2021		0.5	0.5
2022		0.5	0.5
2023		0.5	0.5
2024		0.5	0.5
2025 and beyond		2.4	2.4
Total lease payments		4.7	4.7
Less: Interest		(0.9)	(0.9)
Present value of lease liabilities		$ 3.8	$ 3.8
Future minimum rental commitments under non-cancelable operating leases [Abstract]
2020				14.2
2021				12.4
2022				9.1
2023				7.1
2024				4.7
2025 and beyond				22.9
Total future minimum rental commitments				70.4
Rental expense				$ 19.3	$ 18.5
Minimum [Member]
Significant Accounting Policy [Abstract]
Remaining lease term			1 year
Maximum [Member]
Significant Accounting Policy [Abstract]
Remaining lease term			15 years

[1] Finance lease ROU assets were recorded net of accumulated amortization of $1.5 million as of September 30, 2019.

[2] For the three and six months ended September 30, 2019, operating lease expense included short-term lease expense of $1.0 million and $1.9 million, respectively. Variable lease expense was not significant.