Goodwill and Intangible Assets Goodwill and Intangible Assets (Phantom) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Amortizing Intangibles:
Finite-Lived Intangible Assets, Amortization Expense, Year Two	$ 4.6
Finite-Lived Intangible Assets, Amortization Expense, Year Three	4.6
Amortization expense, year four	4.6
Finite-Lived Intangible Assets, Amortization Expense, Year Five	4.6
Finite-Lived Intangible Assets, Amortization Expense, after Year Five	$ 21.3
Purchased technology, customer relationships and patents | Minimum
Amortizing Intangibles:
Useful life	3 years	3 years
Purchased technology, customer relationships and patents | Maximum
Amortizing Intangibles:
Useful life	18 years	18 years