Debt - Term Loans (Narrative) (Details) - USD ($)
 3 Months Ended 9 Months Ended 12 Months Ended
Aug. 31, 2020
Sep. 30, 2020
Sep. 30, 2020
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Jun. 27, 2017
Line of Credit Facility [Line Items]              
Final payment fee       $ 2,300,000      
Class of warrant or right, number of securities called by warrants or rights (in shares) 196,850            
Exercise price (in dollars per share) $ 2.54     $ 1.62 $ 1.60 $ 1.12  
Class of warrant or right, expiration period 10 years            
Issuance of common warrants with long-term debt, net $ 400,000       $ 444,000    
Loss on extinguishment of debt       $ 0 461,000 $ 0  
Interest expense related to term loans       $ 2,800,000 1,600,000 $ 1,500,000  
Warrants to purchase common stock              
Line of Credit Facility [Line Items]              
Exercise price (in dollars per share)             $ 17.71
2020 Term Loans              
Line of Credit Facility [Line Items]              
Maximum borrowing capacity 35,000,000            
Debt instrument, additional accrued interest in the event of default       0.050      
Debt instrument, redemption price, percentage of principal amount redeemed       9.00%      
Debt instrument, default, bankruptcy, or insolvency value of triggering accelerated redemption 500,000            
Debt issuance costs, line of credit arrangements (less than) 400,000            
Term loan facility       $ 25,000,000.0 $ 25,000,000.0    
2020 Term Loans | Maximum              
Line of Credit Facility [Line Items]              
Debt instrument, prepayment fee, percentage       0.030      
2020 Term Loans | Minimum              
Line of Credit Facility [Line Items]              
Debt instrument, prepayment fee, percentage       0.010      
2020 Term Loans | Debt Instrument, Redemption, Period One              
Line of Credit Facility [Line Items]              
Basis spread on variable rate       7.90%      
2020 Term Loans | Debt Instrument, Redemption, Period Two              
Line of Credit Facility [Line Items]              
Basis spread on variable rate       4.65%      
2020 Term Loans | Debt Instrument, Redemption, Period Three              
Line of Credit Facility [Line Items]              
Basis spread on variable rate       10.00%      
Term A Loans              
Line of Credit Facility [Line Items]              
Maximum borrowing capacity 25,000,000            
Term B Loans              
Line of Credit Facility [Line Items]              
Maximum borrowing capacity 10,000,000            
2017 Term Loans              
Line of Credit Facility [Line Items]              
Repayments of lines of credit $ 13,700,000            
Loss on extinguishment of debt   $ 500,000 $ 500,000