Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2014 Customer	Jan. 31, 2013 Customer	Jan. 31, 2014 Customer	Jan. 31, 2013 Customer	Apr. 30, 2013 Customer
Significant Accounting Policies [Line Items]
Number of clients that accounted for more than 10% of account receivables	0		0		0
Number of clients that accounted for more than 10% of revenue	0	0	0	0
Bad Debts
Significant Accounting Policies [Line Items]
Prior period reclassification adjustment		$ 0.9		$ 1.7
Information Technology
Significant Accounting Policies [Line Items]
Prior period reclassification adjustment		$ 1.1		$ 2.7