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Basis of presentation and significant accounting policies (Details) - Revenue
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Huawei Technologies    
Concentration Risk [Line Items]    
Percentage of concentration of credit risk 52.00% 49.00%
Other Customer    
Concentration Risk [Line Items]    
Percentage of concentration of credit risk 10.00% 10.00%
Top Five Customers    
Concentration Risk [Line Items]    
Percentage of concentration of credit risk 85.00% 87.00%