Subsequent Events (Details) $ in Millions		3 Months Ended					9 Months Ended
	Nov. 22, 2017 USD ($) Position	Jan. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	Apr. 30, 2018 USD ($)	Jan. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)
Subsequent Event [Line Items]
Restructuring charges							$ 0.5
Subsequent Event
Subsequent Event [Line Items]
Expected termination of workforce, percent	13.00%
Employees expected to be terminated | Position	1,150
Minimum | Subsequent Event
Subsequent Event [Line Items]
Expected restructuring and related costs	$ 135.0
Maximum | Subsequent Event
Subsequent Event [Line Items]
Expected restructuring and related costs	149.0
One-time Termination Benefits | Minimum | Subsequent Event
Subsequent Event [Line Items]
Expected restructuring and related costs	124.0
One-time Termination Benefits | Maximum | Subsequent Event
Subsequent Event [Line Items]
Expected restructuring and related costs	137.0
Facility Costs
Subsequent Event [Line Items]
Restructuring charges							$ 0.3
Facility Costs | Minimum | Subsequent Event
Subsequent Event [Line Items]
Expected restructuring and related costs	11.0
Facility Costs | Maximum | Subsequent Event
Subsequent Event [Line Items]
Expected restructuring and related costs	$ 12.0
Scenario, Forecast
Subsequent Event [Line Items]
Restructuring charges		$ 1.0
Scenario, Forecast | Minimum
Subsequent Event [Line Items]
Restructuring charges			$ 8.0	$ 14.0	$ 21.0	$ 91.0
Scenario, Forecast | Maximum
Subsequent Event [Line Items]
Restructuring charges			$ 9.0	$ 15.0	$ 24.0	$ 100.0