| Disaggregation of revenue | 
    |   | 
      | 
    Three Months Ended June 30, | 
      | 
      | 
    Six Months Ended June 30, | 
      | 
 
    |   | 
      | 
    2020 | 
      | 
      | 
    2019 | 
      | 
      | 
    2020 | 
      | 
      | 
    2019 | 
      | 
 
    | Sponsorships and advertising | 
      | 
    $ | 
    285,000 | 
      | 
      | 
    $ | 
    220,000 | 
      | 
      | 
    $ | 
    513,000 | 
      | 
      | 
    $ | 
    458,000 | 
      | 
 
    | Direct to Consumer | 
      | 
      | 
    39,000 | 
      | 
      | 
      | 
    3,000 | 
      | 
      | 
      | 
    54,000 | 
      | 
      | 
      | 
    14,000 | 
      | 
 
    |   | 
      | 
    $ | 
    324,000 | 
      | 
      | 
    $ | 
    223,000 | 
      | 
      | 
    $ | 
    567,000 | 
      | 
      | 
    $ | 
    472,000 | 
      | 
 
 
 | 
| Noncash stock-based compensation expense | 
 Noncash stock-based compensation expense for
the periods presented was comprised of the following: 
  
    |   | 
      | 
    
         Three Months 
        Ended June 30, 
 | 
      | 
      | 
    
         Six Months 
        Ended June 30, 
 | 
      | 
 
    |   | 
      | 
    2020 | 
      | 
      | 
    2019 | 
      | 
      | 
    2020 | 
      | 
      | 
    2019 | 
      | 
 
    | Stock options | 
      | 
    $ | 
    122,000 | 
      | 
      | 
    $ | 
    1,339,000 | 
      | 
      | 
    $ | 
    435,000 | 
      | 
      | 
    $ | 
    2,631,000 | 
      | 
 
    | Warrants | 
      | 
      | 
    60,000 | 
      | 
      | 
      | 
    367,000 | 
      | 
      | 
      | 
    282,000 | 
      | 
      | 
      | 
    1,654,000 | 
      | 
 
    | Restricted stock units | 
      | 
      | 
    190,000 | 
      | 
      | 
      | 
    85,000 | 
      | 
      | 
      | 
    333,000 | 
      | 
      | 
      | 
    236,000 | 
      | 
 
    | Earn-out compensation expense | 
      | 
      | 
    25,000  | 
      | 
      | 
      | 
    8,000  | 
      | 
      | 
      | 
    49,000  | 
      | 
      | 
      | 
    8,000  | 
      | 
 
    | Total noncash stock compensation expense | 
      | 
    $ | 
    397,000 | 
      | 
      | 
    $ | 
    1,799,000 | 
      | 
      | 
    $ | 
    1,099,000 | 
      | 
      | 
    $ | 
    4,529,000 | 
      | 
 
 
  
Noncash stock-based compensation expense for
the periods presented was included in the following financial statement line items:  
  
    |   | 
      | 
    
         Three Months 
        Ended June 30, 
 | 
      | 
      | 
    
         Six Months 
        Ended June 30, 
 | 
      | 
 
    |   | 
      | 
    2020 | 
      | 
      | 
    2019 | 
      | 
      | 
    2020 | 
      | 
      | 
    2019 | 
      | 
 
    | Sales, marketing and advertising | 
      | 
    $ | 
    197,000 | 
      | 
      | 
    $ | 
    196,000 | 
      | 
      | 
    $ | 
    395,000 | 
      | 
      | 
    $ | 
    328,000 | 
      | 
 
    | Technology platform and infrastructure    | 
      | 
      | 
    59,000 | 
      | 
      | 
      | 
    27,000 | 
      | 
      | 
      | 
    148,000 | 
      | 
      | 
      | 
    24,000 | 
      | 
 
    | General and administrative    | 
      | 
      | 
    141,000  | 
      | 
      | 
      | 
    1,576,000  | 
      | 
      | 
      | 
    556,000  | 
      | 
      | 
      | 
    4,177,000  | 
      | 
 
    | Total noncash stock compensation expense | 
      | 
    $ | 
    397,000 | 
      | 
      | 
    $ | 
    1,799,000 | 
      | 
      | 
    $ | 
    1,099,000 | 
      | 
      | 
    $ | 
    4,529,000 | 
      | 
 
 
  
 |