Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Summary of Financial Instruments Measured on a Recurring Basis (Details)

v3.19.1
Fair Value Measurements - Summary of Financial Instruments Measured on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets $ 11,767 $ 11,469
Fair value of financial liabilities 986 3,872
Warrant liability    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial liabilities 986 3,872
Cash on deposit    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets   1,316
Money market funds    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 11,226 10,153
Cash    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 213  
Restricted cash    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 328  
Quoted Prices in Active Markets for Identical Assets (Level 1)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 11,767 11,469
Fair value of financial liabilities 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Warrant liability    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial liabilities 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash on deposit    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets   1,316
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 11,226 10,153
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 213  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Restricted cash    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 328  
Significant Other Observable Inputs (Level 2)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 0 0
Fair value of financial liabilities 0 0
Significant Other Observable Inputs (Level 2) | Warrant liability    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial liabilities 0 0
Significant Other Observable Inputs (Level 2) | Cash on deposit    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets   0
Significant Other Observable Inputs (Level 2) | Money market funds    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 0 0
Significant Other Observable Inputs (Level 2) | Cash    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 0  
Significant Other Observable Inputs (Level 2) | Restricted cash    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 0  
Significant Unobservable Inputs (Level 3)    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 0 0
Fair value of financial liabilities 986 3,872
Significant Unobservable Inputs (Level 3) | Warrant liability    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial liabilities 986 3,872
Significant Unobservable Inputs (Level 3) | Cash on deposit    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets   0
Significant Unobservable Inputs (Level 3) | Money market funds    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 0 $ 0
Significant Unobservable Inputs (Level 3) | Cash    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets 0  
Significant Unobservable Inputs (Level 3) | Restricted cash    
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]    
Fair value of financial assets $ 0