Common Stock Repurchase Program Additional Information (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Apr. 30, 2017 USD ($) $ / shares shares
Common Stock
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 61.2
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 130.8
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares) | shares	2.2
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 85.48
Common Stock shares remained available for repurchase under repurchase plans (in shares) | shares	24.4