Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	May 31, 2014		May 31, 2013		May 31, 2014		May 31, 2013
Earnings Per Share [Abstract]
Net income	$ 16,776		$ 14,793		$ 29,091		$ 24,503
Weighted average common shares outstanding – basic	54,382		56,005		55,544		56,492
Effect of dilutive employee stock options and unvested restricted stock units	1,371		840		1,476		626
Weighted average common shares - diluted	55,753		56,845		57,020		57,118
Net income per common share - basic	$ 0.31		$ 0.26		$ 0.52		$ 0.43
Net income per common share - diluted	$ 0.30		$ 0.26		$ 0.51		$ 0.43
Anti-dilutive securities excluded	1,025	[1]	3,327	[1]	1,036	[1]	3,877	[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.