Stockholders' Equity (Details) (USD $)	3 Months Ended
	Oct. 31, 2012	Oct. 31, 2011
Treasury stock, shares, acquired	0	2,717,393
Treasury stock, value, acquired, cost method		$ 81,152,000
Average price per share of shares repurchased on the open market		$ 29.86
Payment of accrued repurchases of common stock		2,001,000
Prior targeted annual dividend per share authorized by our Board of Directors		$ 1.00
Targeted annual dividend per share	$ 1.10
Quarterly dividend payment amount per share	$ 0.275
Dividend Declared, Subsequent Event [Member]
Dividends payable, date declared, day, month and year	Dec. 06, 2012
Quarterly dividend payment amount per share	$ 0.275
Dividends payable, date to be paid	Dec. 27, 2012
Dividends payable, date of record	Dec. 17, 2012
Dividend Declared - First [Member]
Dividends payable, date declared, day, month and year	Sep. 26, 2012
Quarterly dividend payment amount per share	$ 0.275
Dividends payable, date to be paid	Nov. 20, 2012
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
Stock repurchase program, remaining authorized repurchase amount	11,268,000
Third Stock Repurchase Program [Member]
Maximum amount authorized by the Board of Directors for the repurchase of shares of the Company's common stock	50,000,000
Date Board of Directors authorized stock repurchase program	Dec. 06, 2012
Stock repurchase program, remaining authorized repurchase amount	$ 61,268,000