Summary of Business and Significant Accounting Policies - Additional Information (Detail) $ in Millions	3 Months Ended		12 Months Ended
	Apr. 30, 2017 USD ($) Customer	Apr. 30, 2016 Customer	Jan. 31, 2017 USD ($)
Accounting Standards Update 2016-09 [Member]
Summary Of Business And Accounting Policies [Line Items]
Net cumulative-effect adjustment on retained earnings			$ 0.7
Accounting Standards Update 2016-09 [Member] | Effect on Provision for Income Taxes [Member]
Summary Of Business And Accounting Policies [Line Items]
Recognition of excess tax benefits	$ 13.9
Customer concentration risk [Member] | Revenues [Member]
Summary Of Business And Accounting Policies [Line Items]
Number of customers | Customer	0	0
Minimum [Member]
Summary Of Business And Accounting Policies [Line Items]
Customer payment period	30 days
Maximum [Member]
Summary Of Business And Accounting Policies [Line Items]
Customer payment period	60 days