Share Repurchase Program (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jan. 31, 2019	Jan. 31, 2019	Jan. 31, 2018	Jul. 31, 2018	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	155,111	353,007
Additional number of shares authorized to repurchase					1,500,000	3,000,000
Number of shares repurchased since inception	5,905,000	5,905,000	5,436,000	5,552,000
Payments for Repurchase of Common Stock	$ 35,000	$ 85,000	$ 0
Value of stock repurchased since inception	$ 357,989	$ 357,989	$ 247,189	$ 272,989
Remaining shares available for repurchase under existing program	1,595,277	1,595,277