Concentration of Risk (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2015 item	Mar. 31, 2014 item	Dec. 31, 2014 item
Revenue | Customer concentration risk
Concentration of risk
Number of customers	1	3
Revenue | Customer concentration risk | One customer
Concentration of risk
Percentage of concentration risk	36.50%	38.10%
Revenue | Customer concentration risk | Second customer
Concentration of risk
Percentage of concentration risk		12.60%
Revenue | Customer concentration risk | Third customer
Concentration of risk
Percentage of concentration risk		10.20%
Consolidated accounts receivable | Credit concentration risk
Concentration of risk
Number of customers	4		2
Consolidated accounts receivable | Credit concentration risk | One customer
Concentration of risk
Percentage of concentration risk	17.10%		21.70%
Consolidated accounts receivable | Credit concentration risk | Second customer
Concentration of risk
Percentage of concentration risk	16.50%		20.40%
Consolidated accounts receivable | Credit concentration risk | Third customer
Concentration of risk
Percentage of concentration risk	13.50%
Consolidated accounts receivable | Credit concentration risk | Fourth customer
Concentration of risk
Percentage of concentration risk	11.40%