Income Taxes - Summary of Difference Between Tax Derived by Applying Federal Statutory Income Tax Rate (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Income Tax Disclosure [Abstract]
U.S. federal taxes at statutory rate									$ (11,257)	$ (18,138)	$ (16,550)
State tax provision									(923)	(1,510)	250
Foreign tax rate differentials									(206)	(123)	(185)
Research and development credit									(1,972)	(1,201)	(1,198)
Stock options									506	1,608	3,752
Nondeductible legal expenses									200	5,796	3,956
Permanent differences and other									(8)	(1,389)	153
Change in valuation allowance									13,714	14,457	8,650
Provision for (benefit from) income taxes	$ (540)	$ 324	$ 258	$ 12	$ (418)	$ 179	$ 130	$ (391)	$ 54	$ (500)	$ (1,172)