Convertible Senior Notes (Parenthetical) (Detail) (4.50% Convertible senior notes (due 2014))	Dec. 31, 2012	Dec. 31, 2011	Nov. 30, 2009
4.50% Convertible senior notes (due 2014)
Debt Instrument [Line Items]
Debt instrument, maturity year	2014	2014
Debt instrument, interest rate	4.50%	4.50%	4.50%