Concentrations of Credit Risk (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 customer	Dec. 31, 2013 customer	Dec. 31, 2012 customer
Concentration Risk
Adjustments to the fair value of derivative contracts due to credit related concerns outside of the normal non-performance risk adjustment	0
Customer concentration | Accounts receivable
Concentration Risk
Concentration risk	87.00%	82.00%
EQT | Sales revenue goods, net
Concentration Risk
Percentage required for qualification as major customer			10.00%
EQT | Customer concentration | Sales revenue goods, net
Concentration Risk
Number of customers	1	1	0
Concentration risk	12.00%	11.00%