Concentration of Risk (Details) - customer	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Revenue | Customer concentration risk | One customer
Concentration of risk
Number of customers	3	2	2	1
Percentage of concentration risk		29.90%	16.40%	33.10%
Revenue | Customer concentration risk | Second customer
Concentration of risk
Number of customers	3	2	2
Percentage of concentration risk		10.00%	14.10%
Revenue | Customer concentration risk | Third customer
Concentration of risk
Number of customers	3
Consolidated accounts receivable | Customer concentration risk | One customer
Concentration of risk
Number of customers			3		3
Consolidated accounts receivable | Customer concentration risk | Second customer
Concentration of risk
Number of customers			3		3
Consolidated accounts receivable | Customer concentration risk | Third customer
Concentration of risk
Number of customers			3		3
Consolidated accounts receivable | Credit concentration risk | One customer
Concentration of risk
Percentage of concentration risk	14.80%		16.50%		22.90%
Consolidated accounts receivable | Credit concentration risk | Second customer
Concentration of risk
Percentage of concentration risk	11.70%		14.50%		12.70%
Consolidated accounts receivable | Credit concentration risk | Third customer
Concentration of risk
Percentage of concentration risk	10.40%		10.80%		11.60%