Note 15 - Employee Stock Option and Retirement Plans - Summary of Restricted Stock Award (Details) - Restricted Stock [Member] - $ / shares	3 Months Ended												8 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, 2017	Aug. 31, 2018		Aug. 31, 2017		Aug. 31, 2016
Restricted stock balance (in shares)				182,000				262,000				313,000		182,000		262,000		313,000
Restricted stock balance, weighted average grant date fair value (in dollars per share)				$ 138.62				$ 126.27				$ 103.34		$ 138.62		$ 126.27		$ 103.34
Restricted stock granted (in shares)	2,536	0	0	961	49,473	0	7,843	5,084	3,944	255	0	93,120		3,497		62,400		97,000
Restricted stock granted, weighted average grant date fair value (in dollars per share)	$ 191.97			$ 182.17	$ 158.46		$ 161.31	$ 151.63	$ 164.77	$ 146.20		$ 159.46		$ 189.28		$ 158.26		$ 159.64
Restricted stock vested (in shares)													(132,194)	(26,599)		(132,000)	[1]	(69,000)	[2]
Restricted stock vested, weighted average grant date fair value (in dollars per share)														$ 155.95	[3]	$ 123.28	[1]	$ 85.04	[2]
Restricted stock canceled/forfeited (in shares)														(16,000)		(10,000)		(79,000)
Restricted stock canceled/forfeited, weighted average grant date (in dollars per share)														$ 116.29		$ 130.32		$ 112.51
Restricted stock balance (in shares)	143,000				182,000				262,000				182,000	143,000		182,000		262,000
Restricted stock balance, weighted average grant date fair value (in dollars per share)	$ 139.34				$ 138.62				$ 126.27				$ 138.62	$ 139.34		$ 138.62		$ 126.27

[1] The 132,194 restricted stock awards that vested during fiscal 2017 were comprised of: 73,522 of awards relating to restricted stock granted on November 1, 2013, which cliff vested 60% after three years, 17,328 of awards relating to restricted stock granted on October 16, 2015, which vested 20% annually upon the anniversary date of the grant and 30,162 of awards relating to restricted stock granted on October 16, 2015, which were modified to accelerate vest 100% in conjunction with employee severance. Additionally, 11,182 awards vested related to other grants.

[2] The 69,244 restricted stock awards that vested during fiscal 2016 were comprised of: 37,079 of awards relating to restricted stock granted on November 8, 2010 (remaining 40%) and 14,683 restricted stock awards that were granted on April 8, 2013, which cliff vest 20% annually upon the anniversary date of the grant. Additionally, 17,482 awards vested related to other grants.

[3] The 26,599 restricted stock awards that vested during fiscal 2018 were comprised of: 9,765 of awards relating to restricted stock granted on October 16, 2015 and 8,600 of awards relating to restricted stock granted on June 30, 2017 which vest at a rate of 20% annually upon the anniversary date of the grant, respectively. Additionally, 8,234 awards vested related to other grants.