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Income Taxes - Narrative (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Income Tax Disclosure [Abstract]    
Net operating loss carryforwards $ 99,800 $ 72,600
Tax Credit Carryforward [Line Items]    
Deferred tax assets (34,500) (24,100)
Deferred tax assets, decrease in valuation allowance (10,500)  
Change in Federal tax rate due to tax reform 0 3,221
Provisional decrease to valuation allowance 9,600  
Reduction in net deferred tax liability (6,300)  
Federal | R&D Credit Carryforward    
Tax Credit Carryforward [Line Items]    
Tax credit carryforward 1,200 1,000
State | R&D Credit Carryforward    
Tax Credit Carryforward [Line Items]    
Tax credit carryforward $ 1,200 $ 1,100