Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	May 31, 2013		May 31, 2012		May 31, 2013		May 31, 2012
Earnings Per Share [Abstract]
Net income	$ 14,793		$ 14,407		$ 24,503		$ 21,583
Weighted average common shares outstanding – basic	56,005		59,936		56,492		60,736
Effect of dilutive employee stock options and unvested restricted stock units	840		25		626		31
Weighted average common shares - diluted	56,845		59,961		57,118		60,767
Net income per common share - basic	$ 0.26		$ 0.24		$ 0.43		$ 0.36
Net income per common share - diluted	$ 0.26		$ 0.24		$ 0.43		$ 0.36
Anti-dilutive securities excluded	3,327	[1]	7,382	[1]	3,877	[1]	7,269	[1]

[1] Anti-dilutive securities consist of stock options and unvested restricted stock units that were not included in the computation of diluted earnings per share because either the exercise price of the options was greater than the average market price of the common stock or the total assumed proceeds under the treasury stock method resulted in negative incremental shares and thus the inclusion would have been anti-dilutive.