Note 13 - Employee Stock Option and Retirement Plans - Summary of Restricted Stock Award (Details) - Restricted Stock [Member] - $ / shares	3 Months Ended				6 Months Ended
	Feb. 28, 2019		Nov. 30, 2018		Feb. 28, 2019	Feb. 28, 2018
Restricted stock balance (in shares)	131,000		143,000		143,000
Restricted stock balance, weighted average grant date fair value (in dollars per share)	$ 172.48		$ 139.34		$ 139.34
Restricted stock granted (in shares)			41,000			961
Restricted stock granted, weighted average grant date fair value (in dollars per share)			$ 212.66		$ 212.66	$ 182.17
Restricted stock forfeited (in shares)	(1,000)		(1,000)
Restricted stock forfeited, weighted average grant date fair value (in dollars per share)	$ 184.64		$ 200.18
Restricted stock vested (in shares)	(23,000)	[1]	(52,000)	[2]	(75,530)	(14,839)
Restricted stock vested, weighted average grant date fair value (in dollars per share)	$ 136.58		$ 113.44
Restricted stock balance (in shares)	107,000		131,000		107,000
Restricted stock balance, weighted average grant date fair value (in dollars per share)	$ 187.62		$ 172.48		$ 187.62

[1] The majority of the vested restricted stock awards related to the final vesting of awards granted on February 9, 2015, which vested 100% on the four year anniversary date of the grant.

[2] The majority of the vested restricted stock awards related to the final vesting of awards granted on November 1, 2013, which cliff vested 60% after three years on November 1, 2016 and 40% after five years on November 1, 2018.