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Fair Value Measurement (Details) - Fair Value, Recurring - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents $ 1,078,023 $ 1,199,693
Short-term investments 211,766 306,347
Derivative liabilities 163,410 297,160
Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 1,078,023 1,199,693
Short-term investments 211,766 306,347
Derivative liabilities 0 0
Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 0 0
Short-term investments 0 0
Derivative liabilities 0 0
Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 0 0
Short-term investments 0 0
Derivative liabilities $ 163,410 $ 297,160