Income Taxes - Summary of Difference Between Tax Derived by Applying Federal Statutory Income Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Income Tax Disclosure [Abstract]
U.S. federal taxes at statutory rate									$ (8,603)	$ (11,257)	$ (18,138)
State tax provision									(625)	(923)	(1,510)
Foreign tax rate differentials									(108)	(206)	(123)
Research and development credit									(1,473)	(1,972)	(1,201)
Stock options									3,480	506	1,608
Nondeductible legal expenses									0	200	5,796
Permanent differences and other									0	(8)	(1,389)
Return to provision adjustments									9	0	0
Change in valuation allowance									7,358	13,714	14,457
Provision for (benefit from) income taxes	$ 165	$ (163)	$ 124	$ (88)	$ (540)	$ 324	$ 258	$ 12	$ 38	$ 54	$ (500)