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Income Taxes - Additional Information (Details) - USD ($)
 12 Months Ended
Jan. 01, 2018
Dec. 31, 2019
Dec. 31, 2017
Dec. 31, 2018
Dec. 31, 2016
Operating Loss Carryforwards [Line Items]          
Deferred Tax Assets, Tax Credit Carryforwards, Research   $ 42,490,000   $ 35,670,000  
Effective income tax rate reconciliation, at federal statutory income tax rate, percent 21.00% 21.00% 35.00%    
Adjustment of deferred tax (asset) liability, revaluation based on new tax rate     $ 74,300,000    
Unrecognized Tax Benefits, Ending Balance   $ 4,784,000 120,000 $ 2,385,000 $ 120,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total   0      
Deferred Tax Assets Revaluated          
Operating Loss Carryforwards [Line Items]          
Valuation allowance, deferred tax asset, increase (decrease)     $ (74,300,000)    
Domestic Tax Authority          
Operating Loss Carryforwards [Line Items]          
Operating Loss Carryforwards, Total   865,200,000      
Expiring Operating Loss Carryforwards   $ 549,700,000      
Net operating loss carryforwards expiration year   2021      
Indefinite Operating Loss Carryforwards   $ 315,500,000      
Taxable income limitation percentage for operating loss carryforward   80.00%      
Deferred Tax Assets, Tax Credit Carryforwards, Research   $ 33,700,000      
Research and development credit carryforwards expiration year   2022      
State and Local Jurisdiction          
Operating Loss Carryforwards [Line Items]          
Net operating loss carryforwards expiration year   2028      
Deferred Tax Assets, Tax Credit Carryforwards, Research   $ 15,800,000      
State and Local Jurisdiction | California Franchise Tax Board          
Operating Loss Carryforwards [Line Items]          
Operating Loss Carryforwards, Total   125,900,000      
State and Local Jurisdiction | Other State Jurisdiction          
Operating Loss Carryforwards [Line Items]          
Operating Loss Carryforwards, Total   $ 1,100,000,000