Concentration of Risk (Details) - customer	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Revenue | Customer concentration risk
Concentration of Risk
Number of customers	4	3
Revenue | Customer concentration risk | First customer
Concentration of Risk
Percentage of concentration risk	20.90%	16.40%
Revenue | Customer concentration risk | Second customer
Concentration of Risk
Percentage of concentration risk	16.90%	13.40%
Revenue | Customer concentration risk | Third customer
Concentration of Risk
Percentage of concentration risk	14.60%	10.20%
Revenue | Customer concentration risk | Fourth customer
Concentration of Risk
Percentage of concentration risk	10.70%
Consolidated accounts receivable | Customer concentration risk
Concentration of Risk
Number of customers	2
Consolidated accounts receivable | Credit concentration risk
Concentration of Risk
Number of customers			3
Consolidated accounts receivable | Credit concentration risk | First customer
Concentration of Risk
Percentage of concentration risk	21.20%		24.90%
Consolidated accounts receivable | Credit concentration risk | Second customer
Concentration of Risk
Percentage of concentration risk			15.30%
Consolidated accounts receivable | Credit concentration risk | Third customer
Concentration of Risk
Percentage of concentration risk			11.10%
Consolidated accounts receivable | Credit concentration risk | Fourth customer
Concentration of Risk
Percentage of concentration risk	18.30%