Stock Repurchase Plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Jul. 31, 2016	Dec. 04, 2015	Jul. 16, 2008	Mar. 09, 2006
Accelerated Share Repurchases [Line Items]
Number of shares authorized to repurchase	7,500,000		7,500,000					3,000,000
Additional number of shares authorized to repurchase						1,500,000	3,000,000
Treasury Stock, Shares, Acquired	1,317	0	1,317	377,830
Payments for Repurchase of Common Stock			$ 210	$ 40,000
Number of shares repurchased since inception	5,436,294	5,326,941	5,436,294	5,326,941	5,434,977
Value of stock repurchased since inception	$ (247,189)	$ (233,192)	$ (247,189)	$ (233,192)	$ (246,979)
Remaining shares available for repurchase under existing program	2,063,706		2,063,706