Maximum stock option exercise price

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- Definition

Number of participants eligible to participate in option exchange program.

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No definition available.

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- Definition

Number of options exchanged as part of the option exchange program.

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No definition available.

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- Definition

The exercise price of replacement stock options granted in an option exchange.

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No definition available.

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Number of replacement options granted as part of option exchange program.

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No definition available.

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- Definition

Balance held on behalf of employees for future purchases under an Employee Stock Purchase Plan ("ESPP").

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No definition available.

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- Definition

The weighted average exercise price of options canceled and replaced in an option exchange program.

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No definition available.

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- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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- Definition

Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

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No definition available.

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Number of options outstanding, including both vested and non-vested options.

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- Definition

The weighted average of per share prices paid for shares purchased on the open market for issuance to employees under the plan.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

The number of shares purchased on the open market during the period for issuance to employees under the plan.

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- Definition

Percentage of vesting of share-based compensation awards.

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-Publisher FASB
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- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

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No definition available.

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Stockholders' Equity - Additional Information (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Apr. 30, 2017 USD ($) $ / shares shares	Apr. 30, 2016 USD ($) $ / shares shares	Apr. 30, 2015 USD ($) $ / shares shares	Aug. 02, 2016 $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of non-vested shares	6,428,000	4,967,000	3,488,000
Maximum stock option exercise price \| $ / shares				$ 6.11
Number of eligible participants				113
Number of options exchanged				599,517
Weighted average exercise price of options canceled and exchanged \| $ / shares				$ 9.25
Replacement options granted				241,399
Replacement option exercise price \| $ / shares				$ 4.14
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 2 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value \| $	$ 10.5	$ 8.5	$ 6.2
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized \| $	$ 20.0
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	5,548,000	6,688,000	5,093,000
Options granted	749,000	2,947,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value \| $ / shares	$ 1.36	$ 2.06	$ 3.47
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value \| $	$ 0.3	$ 0.4	$ 4.5
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options \| $	0.4	0.9	5.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value \| $	4.3	$ 4.2	$ 6.1
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options \| $	$ 3.4
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 2 months 25 days
Performance Stock Options (PSOs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	839,000	0
Options granted	2,867,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value \| $ / shares	$ 1.45
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options \| $	$ 0.5
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	3 years 1 month 2 days
Two Thousand Five Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	475,879
Common Stock, Capital Shares Reserved for Future Issuance	475,879
2012 Equity incentive plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	5,910,892
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent	110.00%
Number of non-vested shares	6,208,958
Options granted	6,692,386
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent	85.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	2,820,145
Share Based Compensation Arrangement By Share Based Payment Award Amount Held For Future Purchases \| $	$ 0.3
Share-based Compensation Arrangement by Share-based Payment Award, Shares Purchased for Award	613,504
Share-based Compensation Arrangement by Share-based Payment Award, Per Share Weighted Average Price of Shares Purchased \| $ / shares	$ 3.27