Subsequent Event - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Oct. 16, 2012 Subsequent Event Dividend Declared
Subsequent Event [Line Items]
Dividends declared	$ 0.31	$ 0.23	$ 0.93	$ 0.69	$ 0.31
Dividend payable date					Dec. 14, 2012
Dividend payable, stockholders of record date					Nov. 28, 2012
Dividend declared date					Oct. 16, 2012