EARNINGS PER SHARE (Schedule of the Computation of Net Income Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	Aug. 31, 2017	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2015	May 31, 2015	Feb. 28, 2015	Nov. 30, 2014	Aug. 31, 2017	Aug. 31, 2016	Aug. 31, 2015
EARNINGS PER SHARE [Abstract]
Net income	$ 19,798	$ 18,838	$ 27,219	$ 24,869	$ 22,272	$ 16,837	$ 25,942	$ 23,672	$ 22,447	$ 21,195	$ 24,835	$ 20,647	$ 90,724	$ 88,723	$ 89,124
Less: Allocation of income to unvested stockholders													(1,321)	(1,431)	(1,137)
Net earnings available to common stockholders													$ 89,403	$ 87,292	$ 87,987
Basic weighted average shares outstanding													30,020	29,928	29,848
Add dilutive effect of stock options (two-class method)													3	5	7
Diluted average shares outstanding													30,023	29,933	29,855
Basic net income per share	$ 0.64	$ 0.62	$ 0.90	$ 0.82	$ 0.74	$ 0.55	$ 0.85	$ 0.78	$ 0.75	$ 0.70	$ 0.82	$ 0.68	$ 2.98	$ 2.92	$ 2.95
Diluted net income per share	$ 0.64	$ 0.62	$ 0.90	$ 0.82	$ 0.74	$ 0.55	$ 0.85	$ 0.78	$ 0.75	$ 0.70	$ 0.82	$ 0.68	$ 2.98	$ 2.92	$ 2.95