Equity Compensation Plans - Additional Information (Detail) - USD ($)	12 Months Ended
May 31, 2019	May 31, 2018	May 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	3,997,000	1,913,000	2,525,000
Options Exercisable, Weighted Average Exercise Price	$ 40.68	$ 31.23
Compensation expense related to share based awards	$ 5,543,000	$ 4,909,000	$ 5,261,000
Remaining compensation cost to be expensed in future periods for non-vested options	$ 15,880,000
Weighted average expense recognition period	3 years 4 months 24 days
Number of shares purchased by employees	18,330	22,127	24,953
Employee Stock Purchase Plan \| 2011 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant	365,395
Number of shares authorized for grant	712,500
Annual maximum limit percentage of compensation to purchase shares	5.00%
Employee stock purchase plan stock price percentage	10.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	3 years
Stock option contractual terms	5 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option vesting period	5 years
Stock option contractual terms	10 years

Employee Purchase Plan Purchase Price Percentage of Fair Market Value

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Share based compensation arrangement by share based payment award, options, contractual term one.

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

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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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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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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Amount of capitalized and expensed compensation cost from equity-based compensation arrangements.

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

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