Company's Debt Maturities on Calendar Year Basis (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011 2.50% Convertible Notes	May 23, 2011 2.50% Convertible Notes	Dec. 31, 2011 1.875% Convertible Notes	Dec. 31, 2010 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%	1.875%	1.875%	1.875%
Principal amount of long term debt	$ 300.0	$ 300.0	$ 287.5		$ 287.5