Subsequent Events - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 28, 2014 Dividend Declared
Subsequent Event [Line Items]
Dividends declared per common share (usd per share)	$ 0.45	$ 0.45	$ 0.45	$ 0.45	$ 0.45	$ 0.45	$ 0.45	$ 0.45	$ 1.80	$ 1.80	$ 1.80	$ 0.45
Dividend payable date												Mar. 19, 2014
Dividend record date												Mar. 05, 2014