Stockholders' Equity (Details) (USD $)	0 Months Ended		1 Months Ended	3 Months Ended						6 Months Ended
	Feb. 07, 2013	Dec. 15, 2011	Dec. 31, 2012	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Apr. 30, 2013	Apr. 30, 2012
Stockholders' Equity Note [Abstract]
Share Repurchase Program, maximum amount authorized		$ 150,000,000	$ 300,000,000
Share Repurchase Program, remaining authorized amount				184,500,000
Number of common stock repurchased, shares				0	460,000	0	321,000	0	663,000
Cost of common stock repurchased					44,400,000		25,000,000		46,100,000
Average purchase price per share					$ 96.34		$ 77.89		$ 69.60
Dividends on common stock	$ 1,400,000									$ 1,449,000	$ 1,421,000
Cash dividend, per share	$ 0.03
Dividends payable, date of record	Jan. 25, 2013