Investments (Narrative) (Details) (USD $)	3 Months Ended			3 Months Ended			3 Months Ended
	Aug. 31, 2014	Aug. 31, 2013	May 31, 2014	Aug. 31, 2014 Shred-it Partnership	May 31, 2014 Shred-it Partnership	Apr. 30, 2014 Shred-it Partnership	Aug. 31, 2014 Other Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Investments	$ 451,897,000		$ 458,357,000
Equity method investments	15,500,000		29,700,000	341,400,000	341,400,000
Cash surrender value of insurance policies	92,800,000		86,500,000
Cost method investments	2,200,000		800,000
Cost-method investments, losses due to impairment	0	0
Percentage of newly formed partnership owned by Cintas						42.00%
Equity method investment, recorded at fair value						339,400,000
Gain on deconsolidation of Shredding business	6,619,000	0		6,619,000
Dividends received on equity method investment	5,247,000	0					5,247,000
Cash received from sale of equity method investment							35,200,000
Gain on sale of stock of an equity method investment	$ 21,739,000	$ 0					$ 13,600,000