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Summary of Difference Between Tax Benefit Derived by Applying Federal Statutory Income Tax Rate to Net Losses and Expense Recognized In Financial Statements (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 12 Months Ended
Apr. 30, 2013
Jan. 31, 2013
Oct. 31, 2012
Jul. 31, 2012
Apr. 30, 2012
Jan. 31, 2012
Oct. 31, 2011
Jul. 31, 2011
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Reconciliation of Statutory Federal Tax Rate [Line Items]                      
U.S. federal taxes at statutory rate                 $ (22,066) $ (7,996) $ (6,629)
State tax provision                 275 237 152
Foreign tax rate differentials                 (185) (110) (48)
Research and development credit                 (1,198) (613) (586)
Non-deductible transaction costs                 3,956    
Stock options                 3,752 1,448 1,209
Permanent differences and other                 154 382 281
Change in valuation allowance                 14,165 7,463 6,182
Provision for (benefit from) income taxes $ 584 $ (2,293) $ 274 $ 288 $ 343 $ 181 $ 178 $ 109 $ (1,147) $ 811 $ 561