Recently Issued Accounting Standards (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Jan. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenue	$ 559.9	$ 485.7
Capitalized contract cost	93.3
Accumulated deficit	(1,995.8)		$ (2,084.9)
Accounting Standards Update 2014-09 | Impact from the adoption of ASC 606 and 340-40
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenue			87.6
Capitalized contract cost			90.4
Accumulated deficit	$ 155.6		178.0
Retained Earnings | Accounting Standards Update 2016-16
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cumulative increase to accumulated deficit			$ 1.9