Note 14 - Employee Stock Option and Retirement Plans - Summary of Stock Option Activity (Details) - $ / shares	1 Months Ended	3 Months Ended						9 Months Ended
	Jul. 31, 2012	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	May 31, 2017	May 31, 2016
Balance (in shares)		3,699,000	3,833,000	3,364,000				3,364,000
Balance (in dollars per share)		$ 139.27	$ 136.43	$ 129.54				$ 129.54
Granted (in dollars per share)		$ 163.05			$ 152.10			$ 154.01	$ 168.51
Exercised (in shares)		(62,000)	(170,000)	(199,000)
Exercised (in dollars per share)		$ 93.25	$ 89.62	$ 74.56
Forfeited (in shares)		(52,000)	(50,000)	(26,000)
Forfeited (in dollars per share)		$ 151.65	$ 141.50	$ 147.22
Balance (in shares)		3,597,000	3,699,000	3,833,000				3,597,000
Balance (in dollars per share)		$ 139.97	$ 139.27	$ 136.43				$ 139.97
Non Performance Based [Member]
Granted (in shares)		11,604		671,263	103,903	4,073	513,785
Granted (in dollars per share)		$ 163.05		$ 152.28
Performance Shares [Member]
Granted (in shares)	241,546		61,744	22,460			530,418
Granted (in dollars per share)			$ 169.16	$ 159.45
Non-Employee Director Grant [Member]
Granted (in shares)			24,000
Granted (in dollars per share)			$ 170.24