Net Income Per Common Share (Parenthetical) (Detail) (USD $)	12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2010 Convertible Notes	Dec. 31, 2012 Convertible Notes	Dec. 31, 2011 Convertible Notes	Dec. 31, 2010 Convertible Notes Hedge Warrant	Dec. 31, 2012 Convertible Notes Hedge Warrant	Dec. 31, 2011 Convertible Notes Hedge Warrant	Mar. 31, 2009 Convertible Notes Hedge Warrant
Net Income Loss Per Common Share
Initial debt conversion price	$ 5.48		$ 5.48	$ 5.48	$ 7.67	$ 7.67	$ 7.67	$ 7.67
Shares that would be issued upon conversion	34,703,196	34,700,000			34,700,000