Convertible Senior Notes (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Issued Convertible Senior Notes, net proceeds following underwriting expenses		$ 582,000,000
Convertible senior notes, contingent beneficial conversion feature	60,087,000
Convertible Senior Notes 4.00 Percent Due 2015 [Member]
Debt Instrument [Line Items]
Issued Convertible Senior Notes, aggregate principal amount		600,000,000
Senior debt maturity date		Feb. 15, 2015
Issued Convertible Senior Notes, interest rate		4.00%
Issued Convertible Senior Notes, frequency of interest payments per year		2
Issued Convertible Senior Notes, net proceeds following underwriting expenses		582,000,000
Convertible Senior Notes convertible into Common Stock, initial conversion rate, number of shares	46.607
Convertible senior notes convertible into common stock, subsequent conversion rate, number of shares	62.2331
Convertible senior notes, principal amount applicable for conversion rate	1,000
Convertible senior notes convertible into Common Stock, initial conversion price	$ 21.456
Convertible senior notes convertible into common stock, subsequent conversion price	$ 16.0686
Convertible senior notes, contingent beneficial conversion feature	60,087,000
Convertible senior notes, market value	$ 685,500,000	$ 699,200,000