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Related party transactions (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Nov. 30, 2015
Related Party Transaction [Line Items]      
Proceeds from issuance of convertible promissory notes   $ 6,800,000  
Convertible Promissory Notes [Member]      
Related Party Transaction [Line Items]      
Proceeds from issuance of convertible promissory notes   6,800,000  
Preferred stock investors | Convertible Promissory Notes [Member]      
Related Party Transaction [Line Items]      
Proceeds from issuance of convertible promissory notes   3,800,000  
License agreement      
Related Party Transaction [Line Items]      
Related party transaction, expenses $ 100,000 200,000  
Due to related party 0 0  
Broadband services agreement      
Related Party Transaction [Line Items]      
Related party transaction, expenses $ 200,000 $ 200,000  
Monthly cash fee payment     $ 20,000