Declaration of Special Cash Dividend - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012
Equity [Abstract]
Cash dividend declared per common share	$ 0.75	$ 0.60	$ 0.75	$ 0.60	$ 0.75	$ 0.60
Dividend payment date	Nov. 07, 2013	Nov. 07, 2012
Dividend record date	Oct. 15, 2013	Oct. 11, 2012