Stockholders' Equity (Details) (USD $)	3 Months Ended
	Oct. 31, 2011	Oct. 31, 2010
Treasury Stock, Shares, Acquired	2,717,393	720,996
Treasury Stock, Value, Acquired, Cost Method	$ 81,152,000	$ 20,198,000
Average price per share of shares repurchased on the open market	$ 29.86	$ 28.01
Amount at period end that remains to be expended under the current board repurchase authorization	147,402,000
Targeted annual dividend per share, prior	$ 1.00
Targeted annual dividend per share	$ 1.10	$ 1.00
Dividend Declared [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
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	Dec. 08, 2011
Quarterly dividend payment amount per share	$ 0.275