Summary of Difference Between Tax Derived by Applying Federal Statutory Income Tax Rate (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Reconciliation of Statutory Federal Tax Rate [Line Items]
U.S. federal taxes at statutory rate									$ (18,138)	$ (16,550)	$ (7,996)
State tax provision									(1,510)	250	237
Foreign tax rate differentials									(123)	(185)	(110)
Research and development credit									(1,201)	(1,198)	(613)
Stock options									1,608	3,752	1,448
Nondeductible legal expenses									5,796	3,956
Permanent differences and other									(1,389)	153	382
Change in valuation allowance									14,457	8,650	7,463
Provision for (benefit from) income taxes	$ (418)	$ 179	$ 130	$ (391)	$ 583	$ (2,295)	$ 271	$ 269	$ (500)	$ (1,172)	$ 811