Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Schedule of Income Taxes [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 6,290	$ 6,485
Excess Tax Benefit From Share Based Compensation Not Yet Recognized	33,800
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	7,358	13,714	$ 14,457
Undistributed Earnings of Foreign Subsidiaries	8,100	6,600	5,100
Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings of Foreign Subsidiaries	$ 2,800	2,300	$ 1,700
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	34.00%
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 4,200
Internal Revenue Service (IRS) [Member]
Schedule of Income Taxes [Line Items]
Operating Loss Carryforwards	209,400	192,600
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 9,200	7,700
Operating Loss Carryforward Expiration Year	2026
State and Local Jurisdiction [Member]
Schedule of Income Taxes [Line Items]
Operating Loss Carryforwards	$ 118,600	110,200
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 3,500	$ 2,600
Operating Loss Carryforward Expiration Year	2016
Tax Credit Carry forwards Expiration Date	2033