Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Jul. 31, 2018	Jan. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017	Oct. 31, 2019	Oct. 31, 2018
Income Taxes [Line Items]
Net discrete tax benefit from remeasurement of deferred taxes at new rate due to Tax Act	$ 4.2	$ 28.5	$ 15.8	$ 21.5	$ 15.8
One-time transition tax on deemed repatriation of indefinitely reinvested earnings		$ 7.0
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Increase in Provisional Income Tax Expense (Benefit)	(0.2)
Unrecognized tax benefits, interest on income tax expense	0.7		$ 1.2	0.6	1.2
Income tax benefit related to vesting of share-based compensation awards	$ 1.6			3.1	2.7
Effective Income Tax Reconciliation, Deduction Energy Efficient Government Buildings, Amount				2.6
Discrete tax benefit related to enactment of Tax Act				4.1
Increase (decrease) in tax credits, work opportunity tax credit				$ 1.5	$ 1.8
Forecast
Income Taxes [Line Items]
U.S. statutory federal rate (percent)						21.00%	23.30%