Investments (Narrative) (Details) (USD $)	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012	Apr. 30, 2014 Shred-it Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Investments	$ 458,357,000	$ 101,525,000
Cash surrender value of life insurance policies	86,500,000	73,000,000
Equity method investments	371,100,000	27,600,000
Cost method investments	800,000	900,000
Gain on sale of equity method investments		8,500,000
Cost-method investments, losses due to impairment	0	0	0
Percentage of newly formed partnership owned by Cintas				42.00%
Equity method investment, recorded at fair value				$ 339,400,000