EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended												12 Months Ended
	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, 2014	May 31, 2014	Feb. 28, 2014	Nov. 30, 2013	Aug. 31, 2016	Aug. 31, 2015	Aug. 31, 2014
EARNINGS PER SHARE [Abstract]
Net income	$ 22,272	$ 16,837	$ 25,942	$ 23,672	$ 22,447	$ 21,195	$ 24,835	$ 20,647	$ 21,856	$ 21,320	$ 28,278	$ 21,432	$ 88,723	$ 89,124	$ 92,886
Less: Allocation of income to unvested stockholders													(1,431)	(1,137)	(1,652)
Net earnings available to common stockholders													$ 87,292	$ 87,987	$ 91,234
Basic weighted average shares outstanding													29,928	29,848	29,747
Add dilutive effect of stock options (two-class method)													5	7	10
Diluted average shares outstanding													29,933	29,855	29,757
Basic net income per share	$ 0.74	$ 0.55	$ 0.85	$ 0.78	$ 0.75	$ 0.70	$ 0.82	$ 0.68	$ 0.73	$ 0.70	$ 0.93	$ 0.71	$ 2.92	$ 2.95	$ 3.07
Diluted net income per share	$ 0.74	$ 0.55	$ 0.85	$ 0.78	$ 0.75	$ 0.70	$ 0.82	$ 0.68	$ 0.73	$ 0.70	$ 0.93	$ 0.71	$ 2.92	$ 2.95	$ 3.07