Stockholders' Equity (Details) (USD $)	6 Months Ended
	Jan. 31, 2012	Jan. 31, 2011
Treasury Stock, Shares, Acquired	5,066,292	1,628,848
Treasury Stock, Value, Acquired, Cost Method	$ 155,744,000	$ 46,804,000
Average price per share of shares repurchased on the open market	$ 30.74	$ 28.73
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	72,858,000
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, Day, Month and Year	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, Day, Month and Year	Feb. 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	Mar. 08, 2012
Quarterly dividend payment amount per share	$ 0.275
Dividends Payable, Date to be Paid, Day, Month and Year	May 22, 2012