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Equity and Liability Components of Notes (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Debt Instrument [Line Items]    
Principal amount of convertible notes outstanding $ 449,463 $ 450,250
Unamortized discount of liability component 28,895 30,020
Less: current portion 23,460 3,381
Long-term debt 397,108 416,849
Convertible Senior Notes
    
Debt Instrument [Line Items]    
Principal amount of convertible notes outstanding 150,000 150,000
Unamortized discount of liability component (22,178) (23,082)
Net carrying amount of liability component 127,822 126,918
Less: current portion 0 0
Long-term debt 127,822 126,918
Carrying value of equity component, net of issuance costs $ 20,993 $ 20,993
Remaining amortization period of discount on the liability component 5 years 5 years 3 months 18 days