Significant Risks and Uncertainties Including Business and Credit Concentrations (Details) - customer	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Customer A
Concentration Risk
Concentration risk (as a percent)	73.00%	81.00%	68.00%	76.00%
Customer B
Concentration Risk
Concentration risk (as a percent)	14.00%	13.00%	15.00%	16.00%
Customer D
Concentration Risk
Concentration risk (as a percent)	9.00%	5.00%	12.00%	2.00%
Product Sales | Percentage of sales | Three major customers
Concentration Risk
Number of customers	3	3	3	3
Concentration risk (as a percent)	96.00%	99.00%	95.00%	94.00%