Concentration of Risk (Details) - customer	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Revenue | Customer concentration risk | One customer
Concentration of risk
Number of customers	4	3
Percentage of concentration risk		20.80%	22.00%
Revenue | Customer concentration risk | Second customer
Concentration of risk
Number of customers	4	3
Percentage of concentration risk		13.40%	12.30%
Revenue | Customer concentration risk | Third customer
Concentration of risk
Number of customers	4	3
Percentage of concentration risk		13.20%	12.00%
Revenue | Customer concentration risk | Fourth customer
Concentration of risk
Number of customers			4
Percentage of concentration risk			10.60%
Revenue | Credit concentration risk | One customer
Concentration of risk
Percentage of concentration risk	19.20%
Revenue | Credit concentration risk | Second customer
Concentration of risk
Percentage of concentration risk	16.60%
Revenue | Credit concentration risk | Third customer
Concentration of risk
Percentage of concentration risk	16.40%
Revenue | Credit concentration risk | Fourth customer
Concentration of risk
Percentage of concentration risk	16.30%
Consolidated accounts receivable | Customer concentration risk | One customer
Concentration of risk
Number of customers	3		4
Consolidated accounts receivable | Customer concentration risk | Second customer
Concentration of risk
Number of customers	3		4
Consolidated accounts receivable | Customer concentration risk | Third customer
Concentration of risk
Number of customers	3		4
Consolidated accounts receivable | Customer concentration risk | Fourth customer
Concentration of risk
Number of customers			4
Consolidated accounts receivable | Credit concentration risk | One customer
Concentration of risk
Percentage of concentration risk	24.90%
Consolidated accounts receivable | Credit concentration risk | Second customer
Concentration of risk
Percentage of concentration risk	21.50%
Consolidated accounts receivable | Credit concentration risk | Third customer
Concentration of risk
Percentage of concentration risk	12.70%