Share Repurchase Program (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2018	Apr. 30, 2017	Jul. 31, 2017	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
Treasury Stock, Shares, Acquired	115,422	0	115,422	1,317
Additional number of shares authorized to repurchase						1,500,000	3,000,000
Number of shares repurchased since inception	5,552,000	5,436,000	5,552,000	5,436,000	5,436,000
Payments for Repurchase of Common Stock	$ 25,800		$ 25,800	$ 210
Value of stock repurchased since inception	$ 272,989	$ 247,189	$ 272,989	$ 247,189	$ 247,189
Remaining shares available for repurchase under existing program	1,948,284		1,948,284