Recently Issued Accounting Standards (Adoption of New Accounting Standard - Income Statement) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended			12 Months Ended
		Apr. 30, 2018		Apr. 30, 2017	Jan. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		$ 559.9		$ 485.7
Cost of revenue		66.8		78.2
Marketing and sales		276.4		255.7
Provision for income taxes		(18.6)		(8.2)
Net loss		$ (82.4)		$ (129.6)
Basic net loss per share (in usd per share)		$ (0.38)		$ (0.59)
Diluted net loss per share (in usd per share)		$ (0.38)		$ (0.59)
As Adjusted
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Marketing and sales		$ 262.8
Provision for income taxes		(23.2)
Net loss		$ (60.0)
Basic net loss per share (in usd per share)		$ (0.27)
Diluted net loss per share (in usd per share)		$ (0.27)
Accounting Standards Update 2014-09 | Impact from the adoption of ASC 606 and 340-40
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue					$ 87.6
Marketing and sales		$ 13.6
Provision for income taxes		4.6
Net loss		$ 22.4
Basic net loss per share (in usd per share)		$ 0.11
Diluted net loss per share (in usd per share)		$ 0.11
Maintenance and subscription
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		$ 531.6		$ 437.0
Cost of revenue		50.4		54.9
Maintenance and subscription | As Adjusted
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenue		50.3
Maintenance and subscription | Accounting Standards Update 2014-09 | Impact from the adoption of ASC 606 and 340-40
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Cost of revenue		0.1
Subscription
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		350.4		173.4
Subscription | As Adjusted
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		356.7
Subscription | Accounting Standards Update 2014-09 | Impact from the adoption of ASC 606 and 340-40
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		(6.3)
Maintenance
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		181.2		263.6
Maintenance | As Adjusted
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		186.6
Maintenance | Accounting Standards Update 2014-09 | Impact from the adoption of ASC 606 and 340-40
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		(5.4)
Other
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		28.3	[1]	48.7
Cost of revenue	[2]	12.8		$ 18.6
Other | As Adjusted
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		30.2
Cost of revenue		13.1
Other | Accounting Standards Update 2014-09 | Impact from the adoption of ASC 606 and 340-40
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net revenue		(1.9)
Cost of revenue		$ (0.3)

[1] Previously labeled as "License and other" in prior periods.

[2] Previously labeled as "Cost of license and other revenue" in prior periods.