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Commitments and contingencies - Future Minimum Payments under Non-Cancellable Leases (Detail) - USD ($)
Dec. 31, 2019
Dec. 31, 2018
Operating Leased Assets [Line Items]    
2019   $ 6,231
2020   4,527
2021   2,633
Total   $ 13,391
Bandwidth Purchase Commitments [Member]    
Operating Leased Assets [Line Items]    
2019 $ 7,918,000  
2020 3,415,000  
2021 700,000  
Total $ 12,033,000