Income Taxes - Components of Net Deferred Tax Amounts Recognized in Accompanying Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Deferred tax asset:
Bad debts	$ 466	$ 872
Other accruals	2,363	1,138
Charitable contributions	436	509
Stock options	7,300	5,832
State tax credit	2,633	2,347
Net operating losses	66,431	64,998
Research and development credit	6,869	6,290
Deferred rent	2,333	2,513
Deferred revenue	810	1,969
Foreign tax credit	128	128
Total deferred tax asset	89,769	86,596
Less valuation allowance	(78,558)	(73,806)
Net deferred tax assets	11,211	12,790
Deferred tax liability:
Amortization of intangible assets	(2,854)	(3,564)
Depreciation	(6,628)	(7,476)
Total deferred tax liability	(9,482)	(11,040)
Total net deferred tax assets	$ 1,729	$ 1,750