Annual report pursuant to Section 13 and 15(d)

Summary of significant accounting policies - Additional Information (Details)

v3.20.4
Summary of significant accounting policies - Additional Information (Details)
12 Months Ended
Dec. 31, 2020
USD ($)
segment
Dec. 31, 2019
USD ($)
Accounting Policies [Abstract]    
Joint venture, percent owned 51.00%  
Allowance for doubtful accounts $ 418,000 $ 75,000
Impairment of long-lived assets $ 251,906 0
Number of operating segments | segment 2  
Advertising expense $ 23,000 142,000
Research and development $ 767,000 $ 1,460,000