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