Goodwill, Service Contracts and Other Assets - Information Regarding Service Contracts and Other Assets (Details) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2015	May 31, 2014
Information regarding service contracts and other assets
Service contracts, net	$ 44,824us-gaap_FiniteLivedIntangibleAssetsNet	$ 55,675us-gaap_FiniteLivedIntangibleAssetsNet
Other assets, carrying amount	65,537ctas_OtherAssetsGross	72,906ctas_OtherAssetsGross
Other assets, accumulated amortization	47,458	53,280
Other assets, net	18,079us-gaap_OtherAssetsNoncurrent	19,626us-gaap_OtherAssetsNoncurrent
Noncompete and consulting agreements
Information regarding service contracts and other assets
Other assets, carrying amount	41,709	49,080
Other assets, accumulated amortization	40,127	47,036
Other assets, net	1,582	2,044
Other
Information regarding service contracts and other assets
Other assets, carrying amount	23,828	23,826
Other assets, accumulated amortization	7,331	6,244
Other assets, net	16,497	17,582
Service Contracts
Information regarding service contracts and other assets
Service contracts, carrying amount	340,002	360,634
Service contracts, accumulated amortization	295,178	304,959
Service contracts, net	$ 44,824	$ 55,675

This element represents the accumulated amortization of finite-lived assets and other noncurrent assets.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the gross carrying amount, as of the balance sheet date, of finite-lived assets and other noncurrent assets.

+ References

No definition available.

+ Details

Name:	ctas_OtherAssetsGross
Namespace Prefix:	ctas_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Details

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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate carrying amount, as of the balance sheet date, of noncurrent assets not separately disclosed in the balance sheet. Noncurrent assets are expected to be realized or consumed after one year (or the normal operating cycle, if longer).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 17

-Article 5

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Details

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- Details

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- Details

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