Summary of Significant Accounting Policies - Concentration of Risk (Details) - customer	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Total revenue | Customer concentration risk
Concentration of Risk
Number of customers	2	2	3
Total revenue | Customer concentration risk | Ten largest customers
Concentration of Risk
Number of customers	10	10	10
Percentage of concentration risk	69.50%	74.00%	74.10%
Total revenue | Customer concentration risk | Largest customer
Concentration of Risk
Percentage of concentration risk	17.80%	17.90%	18.20%
Total revenue | Customer concentration risk | Second largest customer
Concentration of Risk
Percentage of concentration risk	15.40%	16.40%	14.20%
Total revenue | Customer concentration risk | Third largest customer
Concentration of Risk
Percentage of concentration risk			12.00%
Accounts receivable | Credit concentration risk
Concentration of Risk
Number of customers	2	2
Accounts receivable | Credit concentration risk | Largest customer
Concentration of Risk
Percentage of concentration risk	29.10%	23.80%
Accounts receivable | Credit concentration risk | Second largest customer
Concentration of Risk
Percentage of concentration risk	13.60%	11.90%