Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Schedule of Income Taxes [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 6,869	$ 6,290
Excess Tax Benefit From Share Based Compensation Not Yet Recognized	34,200
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	4,752	7,358	$ 13,714
Undistributed Earnings of Foreign Subsidiaries	9,100	8,100	6,600
Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings of Foreign Subsidiaries	$ 3,200	2,800	$ 2,300
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	34.00%
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 4,500
Internal Revenue Service (IRS) [Member]
Schedule of Income Taxes [Line Items]
Operating Loss Carryforwards	213,900	209,400
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 10,100	9,200
Operating Loss Carryforward Expiration Year	2026
State and Local Jurisdiction [Member]
Schedule of Income Taxes [Line Items]
Operating Loss Carryforwards	$ 122,200	118,600
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 4,000	$ 3,500
Operating Loss Carryforward Expiration Year	2018
Tax Credit Carry forwards Expiration Date	2033