Concentration of Risk (Details) - customer	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Revenue | Customer concentration risk
Concentration of Risk
Number of customers	3	4	3	4
Revenue | Customer concentration risk | First customer
Concentration of Risk
Percentage of concentration risk	22.50%	15.70%	19.70%	14.80%
Revenue | Customer concentration risk | Second customer
Concentration of Risk
Percentage of concentration risk	22.20%	14.20%	18.50%	14.40%
Revenue | Customer concentration risk | Third customer
Concentration of Risk
Percentage of concentration risk	11.60%	12.70%	16.20%	11.40%
Revenue | Customer concentration risk | Fourth customer
Concentration of Risk
Percentage of concentration risk		12.50%		11.20%
Consolidated accounts receivable | Credit concentration risk
Concentration of Risk
Number of customers			2		3
Consolidated accounts receivable | Credit concentration risk | First customer
Concentration of Risk
Percentage of concentration risk			30.30%		24.90%
Consolidated accounts receivable | Credit concentration risk | Second customer
Concentration of Risk
Percentage of concentration risk			21.80%		15.30%
Consolidated accounts receivable | Credit concentration risk | Third customer
Concentration of Risk
Percentage of concentration risk					11.10%