Concentration of Risk (Details) - item	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Revenue | Customer concentration risk
Concentration of risk
Number of customers				1
Revenue | Customer concentration risk | One customer
Concentration of risk
Percentage of concentration risk	29.90%	15.90%	33.10%	33.10%	24.50%
Revenue | Customer concentration risk | Second customer
Concentration of risk
Percentage of concentration risk	10.00%	11.10%			12.50%
Consolidated accounts receivable | Credit concentration risk | One customer
Concentration of risk
Percentage of concentration risk				18.10%		21.70%
Consolidated accounts receivable | Credit concentration risk | Second customer
Concentration of risk
Percentage of concentration risk				17.00%		20.40%
Consolidated accounts receivable | Credit concentration risk | Third customer
Concentration of risk
Percentage of concentration risk				14.30%
Consolidated accounts receivable | Credit concentration risk | Fourth customer
Concentration of risk
Percentage of concentration risk				10.50%