Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Schedule Of Income Taxes [Line Items]
Research and development credit carry-forwards	$ 6,485	$ 3,497
Excess stock based compensation tax deductions	33,700
Net deferred tax assets	10,018	19,710
Income tax benefit		1,400
Deferred tax assets, valuation allowance increase	13,700	14,800
Permanently reinvested undistributed earnings	7,900	5,100	$ 3,700
Permanently reinvested undistributed earnings, tax impact of distribution	$ 2,700	1,700	$ 1,300
Statutory income tax rate	34.00%
Unrecognized tax benefits if recognized, that would affect the effective tax rate	$ 3,200
Internal Revenue Service (IRS)
Schedule Of Income Taxes [Line Items]
Net operating loss carry-forwards	$ 191,900	190,900
Net operating loss carry-forwards, beginning expiration year	2025
Research and development credit carry-forwards	$ 7,700	4,800
Tax credit carry-forwards, beginning expiration year	2026
State and Local Jurisdiction
Schedule Of Income Taxes [Line Items]
Net operating loss carry-forwards	$ 110,200	83,500
Net operating loss carry-forwards, beginning expiration year	2016
Research and development credit carry-forwards	$ 2,600	$ 1,400
Tax credit carry-forwards, beginning expiration year	2034