Summary of Significant Accounting Policies - Additional Information (Details)
$ in Thousands
 12 Months Ended
Jan. 01, 2017
USD ($)
Dec. 31, 2019
USD ($)
segment
Dec. 31, 2019
EUR (€)
segment
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Jan. 01, 2019
USD ($)
Jan. 01, 2018
USD ($)
Summary Of Significant Accounting Policies [Line Items]              
Accumulated deficit   $ (1,381,988)   $ (1,185,368)      
Allowance for doubtful accounts   200   200      
(Loss) gain on foreign currency translation   $ (900)   $ (2,300) $ 3,700    
Threshold percentage for disclosure of revenue and receivables   10.00% 10.00% 10.00% 10.00%    
Advertising Expense   $ 31,100   $ 54,700 $ 34,400    
Number of business segments | segment   1 1        
Operating lease, right-of-use asset   $ 12,379       $ 20,100  
Operating lease liability   $ 13,808       $ 22,100  
401 (K) Plan              
Summary Of Significant Accounting Policies [Line Items]              
Employee contribution limit as a percentage of their eligible compensation   100.00% 100.00%        
Percentage of employer contribution matched of the first employee pay   100.00% 100.00%        
Maximum employee contribution limit as a percentage of their total taxable earnings   5.00% 5.00%        
Employer contribution   $ 14,800   12,100 9,800    
Defined Contribution Plan              
Summary Of Significant Accounting Policies [Line Items]              
Maximum employee contribution limit as a percentage of their total taxable earnings   40.00% 40.00%        
Employer contribution   $ 4,100   $ 4,000 $ 3,700    
Per employee contribution limit | €     € 115,000        
Maximum percentage of employer contribution matched of employee's   18.00% 18.00%        
Time-Based Stock Options              
Summary Of Significant Accounting Policies [Line Items]              
Expiration period   10 years 10 years        
Vesting rights per year (as a percent)   25.00% 25.00%        
Vesting period   4 years 4 years        
Time-Based Stock Options | Non-employee Directors              
Summary Of Significant Accounting Policies [Line Items]              
Expiration period   10 years 10 years        
Vesting period   1 year 1 year        
Time-vested RSUs              
Summary Of Significant Accounting Policies [Line Items]              
Vesting rights per year (as a percent)   25.00% 25.00%        
Vesting period   4 years 4 years        
Minimum              
Summary Of Significant Accounting Policies [Line Items]              
Manufacturing Process period   10 days 10 days        
Maximum              
Summary Of Significant Accounting Policies [Line Items]              
Manufacturing Process period   56 days 56 days        
Manufacturing and royalty revenues | Minimum              
Summary Of Significant Accounting Policies [Line Items]              
Payment terms in number of days   30 days 30 days        
Manufacturing and royalty revenues | Maximum              
Summary Of Significant Accounting Policies [Line Items]              
Payment terms in number of days   90 days 90 days        
VUMERITY | Other Assets | Biogen              
Summary Of Significant Accounting Policies [Line Items]              
Contract assets, noncurrent   $ 5,000          
Contract with customer assets expected to receive period   3 years 3 years        
ASU 2014-09 | Adjustment              
Summary Of Significant Accounting Policies [Line Items]              
Accumulated deficit             $ 818
ASU 2016-09              
Summary Of Significant Accounting Policies [Line Items]              
Cumulative-effect adjustment to reduce accumulated deficit $ 61,500