Common Stock Repurchase Program - Additional Information (Detail) (USD $) In Millions, except Per Share data	3 Months Ended
	Apr. 30, 2011
Common stock and additional paid-in capital
Stockholders Equity Note [Line Items]
Common stock repurchased and retired, shares	1.7
Repurchased shares of its common stock on the open market, value	$ 39.5
Retained Earnings
Stockholders Equity Note [Line Items]
Repurchased shares of its common stock on the open market, value	$ 29.1
Common Stock Repurchase Program
Stockholders Equity Note [Line Items]
Repurchased shares of its common stock on the open market, average repurchase price per share	$ 40.17
Common Stock shares remained available for repurchase under repurchase plans	22.7