Income Taxes Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Jan. 31, 2018
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Percent	25.30%	31.70%
Discrete tax items [Line Items]
Tax Cuts and Jobs Act of 2017 Transition Tax	$ (3.2)		$ 56.0
Transition Tax Estimate Adjustment [Member]
Discrete tax items [Line Items]
Tax Cuts and Jobs Act of 2017 Transition Tax	$ (3.2)
Effective Income Tax Rate Reconciliation, Deduction, Other, Percent	1.70%
Accounting Standards Update 2016-09 [Member]
Discrete tax items [Line Items]
EffectiveIncomeTaxRateReconciliationSharebasedCompensationExcessTaxBenefitAmount		$ 2.4
Effective Income Tax Rate Reconciliation, Deduction, Other, Percent		1.80%