Note 15 - Stock Option and Retirement Plans - Exercise Price Ranges of Outstanding and Exercisable Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015	Aug. 31, 2014
Number Outstanding (in shares)	3,366	3,364	3,117	3,482
Outstanding Weighted Average Remaining Years of Contractual Life (Year)	7 years 146 days
Balance (in dollars per share)	$ 139.29	$ 129.54	$ 100.71	$ 79.67
Outstanding Aggregate Intrinsic Value	$ 74,244
Exercisable Number Exercisable (in shares)	918	970	1,352
Exercisable Weighted Average Exercise Price Per Share (in dollars per share)	$ 105.14	$ 89.42	$ 78.70
Exercisable Aggregate Intrinsic Value	$ 49,668
Range 1 [Member]
Range of Exercise Prices Per Share, Lower Limit (in dollars per share)	$ 87.26
Range of Exercise Prices Per Share, Upper Limit (in dollars per share)	$ 92.22
Number Outstanding (in shares)	627
Outstanding Weighted Average Remaining Years of Contractual Life (Year)	4 years 255 days
Balance (in dollars per share)	$ 91.59
Outstanding Aggregate Intrinsic Value	$ 41,122
Exercisable Number Exercisable (in shares)	536
Exercisable Weighted Average Exercise Price Per Share (in dollars per share)	$ 91.61
Exercisable Aggregate Intrinsic Value	$ 35,146
Range 2 [Member]
Range of Exercise Prices Per Share, Lower Limit (in dollars per share)	$ 94.84
Range of Exercise Prices Per Share, Upper Limit (in dollars per share)	$ 110.31
Number Outstanding (in shares)	306
Outstanding Weighted Average Remaining Years of Contractual Life (Year)	4 years 328 days
Balance (in dollars per share)	$ 99.02
Outstanding Aggregate Intrinsic Value	$ 17,797
Exercisable Number Exercisable (in shares)	240
Exercisable Weighted Average Exercise Price Per Share (in dollars per share)	$ 97.41
Exercisable Aggregate Intrinsic Value	$ 14,345
Range 3 [Member]
Range of Exercise Prices Per Share, Lower Limit (in dollars per share)	$ 131.31
Range of Exercise Prices Per Share, Upper Limit (in dollars per share)	$ 148.52
Number Outstanding (in shares)	540
Outstanding Weighted Average Remaining Years of Contractual Life (Year)	7 years 36 days
Balance (in dollars per share)	$ 135.46
Outstanding Aggregate Intrinsic Value	$ 11,730
Exercisable Number Exercisable (in shares)	4
Exercisable Weighted Average Exercise Price Per Share (in dollars per share)	$ 138.48
Exercisable Aggregate Intrinsic Value	$ 75
Range 4 [Member]
Range of Exercise Prices Per Share, Lower Limit (in dollars per share)	$ 150.81
Range of Exercise Prices Per Share, Upper Limit (in dollars per share)	$ 152.28
Number Outstanding (in shares)	729
Outstanding Weighted Average Remaining Years of Contractual Life (Year)	9 years 36 days
Balance (in dollars per share)	$ 152.25
Outstanding Aggregate Intrinsic Value	$ 3,595
Exercisable Number Exercisable (in shares)	20
Exercisable Weighted Average Exercise Price Per Share (in dollars per share)	$ 152.05
Exercisable Aggregate Intrinsic Value	$ 102
Range 5 [Member]
Range of Exercise Prices Per Share, Lower Limit (in dollars per share)	$ 159.14
Range of Exercise Prices Per Share, Upper Limit (in dollars per share)	$ 170.24
Number Outstanding (in shares)	692
Outstanding Weighted Average Remaining Years of Contractual Life (Year)	8 years 255 days
Balance (in dollars per share)	$ 165.23
Outstanding Aggregate Intrinsic Value
Exercisable Number Exercisable (in shares)	27
Exercisable Weighted Average Exercise Price Per Share (in dollars per share)	$ 164.90
Exercisable Aggregate Intrinsic Value
Range 6 [Member]
Range of Exercise Prices Per Share, Lower Limit (in dollars per share)	$ 171.22
Range of Exercise Prices Per Share, Upper Limit (in dollars per share)	$ 175.20
Number Outstanding (in shares)	472
Outstanding Weighted Average Remaining Years of Contractual Life (Year)	8 years 36 days
Balance (in dollars per share)	$ 173.39
Outstanding Aggregate Intrinsic Value
Exercisable Number Exercisable (in shares)	91
Exercisable Weighted Average Exercise Price Per Share (in dollars per share)	$ 175.20
Exercisable Aggregate Intrinsic Value