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Debt - Additional Information (Detail) (USD $)
 1 Months Ended 3 Months Ended
Jan. 31, 2012
Mar. 31, 2012
Month
Debt Disclosure [Line Items]    
Convertible senior notes, net proceeds   $ 144,316,000
Value of shares in excess of principal amount of Notes based on closing price   42,700,000
Convertible senior notes, repurchase price at option of the issuer 100.00%  
Convertible Senior Notes
    
Debt Disclosure [Line Items]    
Convertible senior notes, principal amount 150,000,000  
Convertible senior notes, stated interest rate 3.50%  
Convertible senior notes, due date 2032  
Convertible senior notes, net proceeds 144,300,000  
Convertible senior notes, payment start date 2012-07-15  
Convertible senior notes, maturity date Jan. 15, 2032  
Additional interest rate on notes per annum   0.50%
Proceeds allocated to conversion option   23,800,000
Fair value of the liability component 150,000,000 126,200,000
Note, estimated remaining life   24 months
Effective interest rate   13.50%
Unamortized debt discount   4,300,000
Debt discount amortization period (in months)   24
Convertible senior notes, carrying amount net of unamortized discount   124,200,000
Convertible senior notes, interest expense   4,000,000
Interest expense, contractual coupon interest accrual   1,200,000
Interest expense, amortization of discount   2,300,000
Convertible Senior Notes | Allocation of the proceeds to the conversion option
    
Debt Disclosure [Line Items]    
Unamortized debt discount   21,500,000
Convertible Senior Notes | Underwriter's discounts and offering costs
    
Debt Disclosure [Line Items]    
Interest expense, amortization of discount   $ 500,000
Convertible Senior Notes | American Depository Shares
    
Debt Disclosure [Line Items]    
Convertible senior notes, exchange rate of ADS per $1,000 principal amount of notes   113.4752
Convertible senior notes, total ADS into which the debt is exchangeable   17,021,280