Subsequent Event - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Aug. 31, 2011	Oct. 31, 2012 Subsequent Event Repurchase of Equity	Oct. 30, 2012 Subsequent Event Repurchase of Equity
Subsequent Event [Line Items]
Common stock repurchase, authorized amount	$ 20	$ 300
Subsequent event date		Oct. 31, 2012
Common stock, shares outstanding			140