STOCKHOLDERS' EQUITY: - Effect of stock-based compensation expense on income, by financial statement line item (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Share-based compensation
Total non-cash stock-based compensation	$ 89.4	$ 102.7	$ 52.9
Cost of revenue
Share-based compensation
Total non-cash stock-based compensation	3.8	4.7	2.7
Research and development
Share-based compensation
Total non-cash stock-based compensation	23.3	28.2	15.6
Sales and marketing
Share-based compensation
Total non-cash stock-based compensation	38.0	44.0	23.4
General and administrative
Share-based compensation
Total non-cash stock-based compensation	$ 24.4	$ 25.8	$ 11.2