Stockholders' Equity (Details) (USD $)	9 Months Ended
	Apr. 30, 2012	Apr. 30, 2011
Treasury Stock, Shares, Acquired	6,054,022	2,365,870
Treasury Stock, Value, Acquired, Cost Method	$ 188,061,000	$ 68,071,000
Average price per share of shares repurchased on the open market	$ 31.06	$ 28.77
Payment of accrued repurchases of common stock	2,001,000
Amount at period end that remains to be expended under the current board repurchase authorization	40,560,000
Targeted annual dividend per share, prior	$ 1.00
Targeted annual dividend per share	$ 1.10	$ 1.00
Dividend Declared - First [Member]
Dividends Payable, Date Declared, Day, Month and Year	Sep. 27, 2011
Quarterly dividend payment amount per share	$ 0.275
Dividends Payable, Date to be Paid	Nov. 22, 2011
Dividend Declared - Second [Member]
Dividends Payable, Date Declared, Day, Month and Year	Dec. 08, 2011
Quarterly dividend payment amount per share	$ 0.275
Dividends Payable, Date to be Paid	Feb. 22, 2012
Dividend Declared - Third [Member]
Dividends Payable, Date Declared, Day, Month and Year	Mar. 08, 2012
Quarterly dividend payment amount per share	$ 0.275
Dividends Payable, Date to be Paid	May 22, 2012
First stock repurchase program [Member]
Maximum amount authorized by the board of directors for the repurchase of shares of the company's common stock		100,000,000
Second stock repurchase program [Member]
Maximum amount authorized by the board of directors for the repurchase of shares of the company's common stock	$ 250,000,000
Dividend Declared, Subsequent Event [Member]
Dividends Payable, Date Declared, Day, Month and Year	Jun. 07, 2012
Quarterly dividend payment amount per share	$ 0.275
Dividends Payable, Date to be Paid	Aug. 20, 2012