STOCK-BASED COMPENSATION: Stock-based compensation activity, by award type (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Share-based compensation
Other non-employee stock-based compensation	$ 0.6	$ 0.6
Total non-cash stock-based compensation	40.7	42.0
Total non-cash stock-based compensation included in the consolidated statements of equity	27.9	31.3
Stock options
Share-based compensation
Share-based compensation expense	1.4	1.8
Restricted stock units
Share-based compensation
Share-based compensation expense	24.8	25.4
Arbor Holdback Agreement | Arbor
Share-based compensation
Share-based compensation expense	0.0	2.6
Consideration Holdback | Data Plus Math Corporation
Share-based compensation
Share-based compensation expense	4.0	2.1
Pacific Data Partners, LLC Agreement Plan | Pacific Data Partners LLC
Share-based compensation
Share-based compensation expense	9.2	9.5
Liability-based equity awards
Share-based compensation
Total non-cash stock-based compensation	(12.8)	(10.7)
Acuity Performance Earnout | Acuity Data
Share-based compensation
Share-based compensation expense	$ 0.7	$ 0.0