Stockholders' Equity - Assumptions Used to Estimate Fair Value of Options and ESSP Using Black-Scholes Option Pricing Model (Details)	12 Months Ended
Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	37.00%	42.00%	43.00%
Expected volatility, maximum	38.00%	42.00%	50.00%
Risk-free interest rate, minimum	0.97%	1.50%	1.46%
Risk-free interest rate, maximum	1.93%	1.92%	1.93%
Expected term		6 years	6 years
Dividend yield	0.00%	0.00%	0.00%
Stock Options \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	3 years 9 months 20 days
Stock Options \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	4 years 7 months
Performance Stock Options (PSOs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	38.00%	0.00%	0.00%
Expected volatility, maximum	40.00%	0.00%	0.00%
Risk-free interest rate, minimum	1.04%	0.00%	0.00%
Risk-free interest rate, maximum	1.13%	0.00%	0.00%
Expected term		0 years	0 years
Dividend yield	0.00%	0.00%	0.00%
Performance Stock Options (PSOs) [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	4 years 9 months 7 days
Performance Stock Options (PSOs) [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	5 years 3 months 4 days
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	38.00%	30.00%	36.00%
Expected volatility, maximum	51.00%	57.00%	57.00%
Risk-free interest rate, minimum	0.46%	0.10%	0.05%
Risk-free interest rate, maximum	0.89%	0.46%	0.11%
Expected term	6 months	6 months	6 months
Dividend yield	0.00%	0.00%	0.00%

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

No definition available.

+ Details

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- Definition

The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

No definition available.

+ Details

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- Definition

The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

No definition available.

+ Details

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- Definition

The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

+ References

No definition available.

+ Details

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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.

+ References

No definition available.

+ Details

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- Definition

Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

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