Concentration of Risk (Details) - customer	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenue | Customer concentration risk
Concentration of Risk
Number of customers	1	3	2	3
Revenue | Customer concentration risk | First customer
Concentration of Risk
Percentage of concentration risk	26.70%	16.80%	18.50%	18.80%
Revenue | Customer concentration risk | Second customer
Concentration of Risk
Percentage of concentration risk		11.20%	14.10%	15.20%
Revenue | Customer concentration risk | Third customer
Concentration of Risk
Percentage of concentration risk		10.30%		12.10%
Consolidated accounts receivable | Credit concentration risk
Concentration of Risk
Number of customers			1		2
Consolidated accounts receivable | Credit concentration risk | First customer
Concentration of Risk
Percentage of concentration risk					23.80%
Consolidated accounts receivable | Credit concentration risk | Second customer
Concentration of Risk
Percentage of concentration risk			32.20%		11.90%