Net Carrying Amount of Debt (Parenthetical) (Detail)	Sep. 30, 2012 2.50% Convertible Notes	Mar. 31, 2012 2.50% Convertible Notes	Dec. 31, 2011 2.50% Convertible Notes	May 23, 2011 2.50% Convertible Notes	Sep. 30, 2012 1.875% Convertible Notes	Dec. 31, 2011 1.875% Convertible Notes	Jun. 20, 2007 1.875% Convertible Notes
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.50%	2.50%	2.50%	2.50%	1.875%	1.875%	1.875%