Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Mar. 12, 2013	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Commitments and Contingencies Disclosure [Line Items]
Rental expense		$ 4.1	$ 1.7	$ 1.3
Damages sought in shareholder derivative action	91.4
Sales tax liability accrual		2.5
Minimum
Commitments and Contingencies Disclosure [Line Items]
Sales tax liability estimate		1.3
Maximum
Commitments and Contingencies Disclosure [Line Items]
Sales tax liability estimate		$ 3.4