Stock Repurchase Plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 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					1,500,000		3,000,000
Treasury Stock, Shares, Acquired	0	0	377,830	0
Payments for Repurchase of Common Stock			$ 40,000	$ 0
Number of shares repurchased since inception	5,326,941	4,949,111	5,326,941	4,949,111		4,949,111
Value of stock repurchased since inception	$ (233,192)	$ (193,192)	$ (233,192)	$ (193,192)		$ (193,192)
Remaining shares available for repurchase under existing program	2,173,059		2,173,059