Stock Repurchase Plan (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2015	Oct. 31, 2014	Dec. 07, 2015	Dec. 04, 2015	Jul. 31, 2015	Jul. 16, 2008	Mar. 09, 2006
Accelerated Share Repurchases [Line Items]
Number of shares authorized to repurchase							3,000,000
Additional number of shares authorized to repurchase						3,000,000
Treasury Stock, Shares, Acquired	377,830	0
Payments for Repurchase of Common Stock	$ 40,000	$ 0
Number of shares repurchased since inception	5,326,941	4,949,111			4,949,111
Value of stock repurchased since inception	$ (233,192)	$ (193,192)			$ (193,192)
Remaining shares available for repurchase under existing program	673,059
Scenario, Forecast [Member]
Accelerated Share Repurchases [Line Items]
Additional number of shares authorized to repurchase				1,500,000
Remaining shares available for repurchase under existing program			2,173,059