Stockholders' Equity (Share Repurchases) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Jul. 31, 2015	Jan. 31, 2015	Jul. 31, 2014	Jan. 31, 2014	Dec. 15, 2011
Equity [Abstract]
Share Repurchase Program, maximum amount authorized					$ 500.0
Number of common stock repurchased, shares	0	100,000	0	396,000
Cost of common stock repurchased		$ 16.0		$ 50.0
Average purchase price per share		$ 159.96		$ 126.21
Share Repurchase Program, remaining authorized amount	$ 169.7