Common Stock Repurchase Program (Additional Information) (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Apr. 30, 2018 USD ($) $ / shares shares
Common Stock
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 16.4
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 4.6
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares) | shares	0.2
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 113.3
Common stock shares remained available for repurchase under repurchase plans (in shares) | shares	19.5