Note 15 - Employee Stock Option and Retirement Plans - Summary of Stock Option Activity (Details) - $ / shares	3 Months Ended												12 Months Ended
	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Feb. 28, 2016	Nov. 30, 2015	Aug. 31, 2018	Aug. 31, 2017	Aug. 31, 2016
Balance (in shares)				3,366,000				3,364,000				3,117,000	3,366,000	3,364,000	3,117,000
Balance (in dollars per share)				$ 139.29				$ 129.54				$ 100.71	$ 139.29	$ 129.54	$ 100.71
Granted (in shares)		0
Granted (in dollars per share)													$ 190.42	$ 156.77	$ 168.55
Exercised (in shares)													(622,000)	(487,000)	(681,000)
Exercised (in dollars per share)													$ 113.73	$ 86.17	$ 71.52
Forfeited (in shares)													(212,000)	(539,000)	(268,000)
Forfeited (in dollars per share)													$ 158.14	$ 160.31	$ 113.70
Balance (in shares)	3,143,000				3,366,000				3,364,000				3,143,000	3,366,000	3,364,000
Balance (in dollars per share)	$ 153.05				$ 139.29				$ 129.54				$ 153.05	$ 139.29	$ 129.54
Balance (in dollars per share)	$ 153.05			$ 139.29	$ 139.29			$ 129.54	$ 129.54			$ 100.71	$ 139.29	$ 129.54	$ 100.71
Non Performance Based [Member]
Granted (in shares)	5,848		15,363	553,942	29,650	11,604		671,263	20,911	103,903	4,073	513,785	575,000	713,000	622,000
Granted (in dollars per share)													$ 190.14	$ 152.89	$ 171.18
Performance Shares [Member]
Granted (in shares)	16,512						61,744	22,460					17,000	291,000	551,000
Granted (in dollars per share)													$ 200.20	$ 166.29	$ 165.59
Non-Employee Director Grant [Member]
Granted (in shares)													19,000	24,000	23,000
Granted (in dollars per share)													$ 197.75	$ 170.24	$ 146.82