STOCK-BASED COMPENSATION - Restricted Stock Unit and Performance-based Restricted Stock Unit - Activity (Details)	12 Months Ended
May 31, 2020 $ / shares shares
Stock-settled restricted stock units
Shares
Outstanding at beginning of the period (in shares)	641,020
Granted (in shares)	232,471
Vested (in shares)	(180,895)
Forfeited/expired/cancelled (in shares)	(30,391)
Outstanding at end of the period (in shares)	662,205
Weighted-Average Grant-Date Fair Value
Outstanding at beginning of the period (in dollars per share) \| $ / shares	$ 49.17
Granted (in dollars per share) \| $ / shares	68.69
Vested (in dollars per share) \| $ / shares	31.57
Forfeited/expired/cancelled (in dollars per share) \| $ / shares	61.16
Outstanding at end of the period (in dollars per share) \| $ / shares	$ 60.28
Cash-settled RSUs
Shares
Outstanding at beginning of the period (in shares)	120,810
Vested (in shares)	(120,810)
Outstanding at end of the period (in shares)	0
Weighted-Average Grant-Date Fair Value
Outstanding at beginning of the period (in dollars per share) \| $ / shares	$ 28.33
Vested (in dollars per share) \| $ / shares	$ 28.33
Performance shares
Shares
Outstanding at beginning of the period (in shares)	314,281
Granted (in shares)	104,250
Performance condition adjustment (in shares)	67,224
Vested (in shares)	(36,532)
Forfeited/expired/cancelled (in shares)	(4,766)
Outstanding at end of the period (in shares)	444,457
Weighted-Average Grant-Date Fair Value
Outstanding at beginning of the period (in dollars per share) \| $ / shares	$ 51.06
Granted (in dollars per share) \| $ / shares	67.90
Performance condition adjustment (in dollars per share) \| $ / shares	60.66
Vested (in dollars per share) \| $ / shares	30.80
Forfeited/expired/cancelled (in dollars per share) \| $ / shares	66.87
Outstanding at end of the period (in dollars per share) \| $ / shares	$ 57.96

The number of performance condition adjustments shares made during the period.

No definition available.

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- Definition

The weighted average fair value at grant date for nonvested performance condition adjustments during the period.

+ References

No definition available.

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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- Definition

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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-Publisher FASB
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-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Paragraph 2
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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).

+ References

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

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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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Paragraph 2
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- Definition

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

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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