Income Taxes - Components of Net Deferred Tax Amounts Recognized in Accompanying Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Apr. 30, 2016	Apr. 30, 2015
Deferred tax asset:
Bad debts	$ 872	$ 1,493
Other accruals	1,138	1,317
Charitable contributions	509	352
Stock options	5,832	5,412
State tax credit	2,347	496
Net operating losses	64,998	58,822
Research and development credit	6,290	6,485
Deferred rent	2,513	273
Deferred revenue	1,969	1,816
FTC	128	0
Total deferred tax asset	86,596	76,466
Less valuation allowance	(73,806)	(66,448)
Net deferred tax assets	12,790	10,018
Deferred tax liability:
Amortization of intangible assets	(3,564)	(4,300)
Depreciation	(7,476)	(4,374)
Total deferred tax liability	(11,040)	(8,674)
Total net deferred tax assets	$ 1,750	$ 1,344