STOCK-BASED COMPENSATION: - Effect of stock-based compensation expense on income, by financial statement line item (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Share-based compensation
Total non-cash stock-based compensation	$ 40.7	$ 42.0
Cost of revenue
Share-based compensation
Total non-cash stock-based compensation	1.7	1.8
Research and development
Share-based compensation
Total non-cash stock-based compensation	13.6	10.0
Sales and marketing
Share-based compensation
Total non-cash stock-based compensation	16.4	18.7
General and administrative
Share-based compensation
Total non-cash stock-based compensation	$ 9.0	$ 11.5