Summary of Restricted Common Share Activity (Detail) - Restricted Common Shares - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
May. 31, 2015	May. 31, 2014	May. 31, 2013
Restricted Common Shares
Outstanding, beginning of year	573	399	513
Granted	240	380	121
Vested	(142)	(185)	(233)
Forfeited	(36)	(21)	(2)
Outstanding, end of year	635	573	399
Weighted Average Grant Date Fair Value
Outstanding, beginning of year	$ 28.36	$ 18.74	$ 17.08
Granted	40.05	33.14	20.76
Vested	23.32	17.17	16.10
Forfeited	32.62	30.70	22.09
Outstanding, end of year	$ 33.65	$ 28.36	$ 18.74
Weighted Average Remaining Contractual Life (in years)
Weighted average remaining contractual life of outstanding restricted common shares (in years)	1 year 4 months 28 days	1 year 7 months 10 days	1 year 3 months 22 days
Aggregate intrinsic value
Aggregate intrinsic value of outstanding restricted common shares	$ 17,269	$ 23,112	$ 13,701
Aggregate intrinsic value of restricted common shares vested during the year	$ 5,400	$ 7,499	$ 5,559

No definition available.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Publisher FASB

-Name Accounting Standards Codification

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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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-Publisher FASB

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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No definition available.

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Intrinsic value of equity-based compensation awards outstanding. Excludes stock and unit options.

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Intrinsic value of equity-based compensation awards vested. Excludes stock and unit options.

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No definition available.

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