Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Statement of Comprehensive Income [Abstract]
Net loss applicable to common stockholders	$ (15,941)	$ (25,339)	$ (34,421)
Other comprehensive loss, net of tax:
Foreign currency translation adjustment	(784)	(255)	(934)
Unrealized gain (loss) on investments	(20)	15	(32)
Total other comprehensive loss, net of tax	(804)	(240)	(966)
Comprehensive loss	$ (16,745)	$ (25,579)	$ (35,387)