Stockholders' Equity (Details) (USD $)	0 Months Ended		1 Months Ended	3 Months Ended
	Feb. 07, 2013	Dec. 15, 2011	Dec. 31, 2012	Jan. 31, 2013	Jul. 31, 2012	Jan. 31, 2012
Stockholders' Equity Note [Abstract]
Share Repurchase Program, maximum amount authorized		$ 150,000,000	$ 300,000,000
Number of common stock repurchased, shares				460,000	321,000	663,000
Cost of common stock repurchased				44,400,000	25,000,000	46,100,000
Share Repurchase Program, remaining authorized amount				184,500,000
Average purchase price per share				$ 96.34	$ 77.89	$ 69.60
Dividends on common stock	$ 1,400,000
Cash dividend, per share	$ 0.03
Dividends payable, date of record	Jan. 25, 2013