Employee Stock Plans - Additional Information (Detail)	3 Months Ended
Jul. 31, 2016 USD ($) $ / shares shares	Jul. 31, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase of common stock \| $	$ 4,161,000	$ 6,573,000
Shares repurchased during the period	0	0
Time Based Restricted Stock \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Time Based Restricted Stock \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Market Based Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Shares outstanding	600,000
Total unrecognized compensation cost related to non-vested awards \| $	$ 11,700,000
Performance Based Restricted Stock Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Shares outstanding	100,000
Total unrecognized compensation cost related to non-vested awards \| $	$ 9,300,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of common stock upon exercise of employee stock options \| $	$ 400,000	$ 1,100,000
Stock Options \| Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock issued for stock options exercised	32,470	71,428
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost related to non-vested awards \| $	$ 41,600,000
Expected cost recognized over weighted-average period	2 years 8 months 12 days
Shares repurchased during the period to pay for taxes	185,754	188,104
Purchase of common stock \| $	$ 4,200,000	$ 6,600,000
Stock Incentive Plan 2008
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares reserved for issuance	5,700,000
Issuance of full-value stock awards limitation, required ratio to stock options	1.91
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares reserved for issuance	3,000,000
Authorized payroll deductions	15.00%
Authorized payroll deductions, value \| $	$ 25,000
Fair market price of common stock	85.00%
Shares available for future issuance	1,400,000
Employees stock purchased	114,011	44,334
Employees stock purchased, price per share \| $ / shares	$ 17.60	$ 29.55

Purchase price paid by employees for common stock through an employee stock purchase plan.

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- Definition

Full Value Stock to Stock Options Ratio

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- Definition

Share-based compensation arrangement by share-based payment award, maximum employee subscription value.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

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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

Amount of cash outflow to satisfy an employee's income tax withholding obligation as part of a net-share settlement of a share-based award.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
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- Definition

The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Discount rate from fair value on purchase date that participants pay for shares.

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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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- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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.

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- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

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Number of shares issued during the period as a result of an employee stock purchase plan.

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Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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Number of shares that have been repurchased during the period and are being held in treasury.

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