Payment of Special Cash Dividend - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Sep. 30, 2013	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012
Equity [Abstract]
Cash dividend declared per common share	$ 0.75	$ 0.75	$ 0.60	$ 0.50
Dividend payment date	Nov. 07, 2013
Dividend record date	Oct. 15, 2013
Cash dividend paid per common share			$ 0.60	$ 0.50