v3.20.4
Income Taxes - Additional Information (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
USD ($)
Ownership
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Income Taxes Disclosure [Line Items]      
Increased in valuation allowance $ 169,700 $ 178,900  
Research and development tax credit carryforwards 104,110 73,442  
Unrecognized tax benefits 29,175 $ 19,487 $ 14,541
Accrued interest and penalties $ 200    
Income tax examination description The Company is currently under examination by Texas Comptroller for calendar tax years 2015, 2016, and 2017. All tax years remain subject to examination by federal and state authorities. These audits include questioning the timing and amount of deductions; the nexus of income among various tax jurisdictions; and compliance with federal, state, and local tax laws.    
Research and Development Credits      
Income Taxes Disclosure [Line Items]      
Unrecognized tax benefits $ 28,300    
Federal      
Income Taxes Disclosure [Line Items]      
Net operating loss carryforwards $ 1,423,100    
Net operating loss carryforwards, expiration beginning year 2028    
Research and development tax credit carryforwards $ 82,600    
Tax credit carryforwards, expiration beginning year 2028    
State      
Income Taxes Disclosure [Line Items]      
Net operating loss carryforwards $ 1,273,900    
Net operating loss carryforwards, expiration year 2020    
Research and development tax credit carryforwards $ 59,400    
Tax credit carryforwards, expiration beginning year 2035    
UK      
Income Taxes Disclosure [Line Items]      
Net operating loss carryforwards $ 17,600    
Research and development tax credit carryforwards 300    
Denmark      
Income Taxes Disclosure [Line Items]      
Net operating loss carryforwards $ 800    
Section 382      
Income Taxes Disclosure [Line Items]      
Number of ownership changes for income tax purposes | Ownership 4    
International      
Income Taxes Disclosure [Line Items]      
Unrecognized tax benefits $ 900