Company's Debt Maturities on Calendar Year Basis (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013 1.50% Convertible Notes	Mar. 18, 2013 1.50% Convertible Notes	Dec. 31, 2012 1.50% Convertible Notes	Jun. 30, 2013 2.50% Convertible Notes	Dec. 31, 2012 2.50% Convertible Notes	May 23, 2011 2.50% Convertible Notes
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	1.50%	1.50%	1.50%	2.50%	2.50%	2.50%
Principal amount of long term debt	$ 400.0	$ 400.0		$ 300.0		$ 300.0