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Commitments and Contingencies (Details)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Revenue | Customer concentration        
Certain Risks and Concentrations        
Concentration Risk, Percentage 70.00% 72.00% 72.00% 67.00%