Summary of Significant Accounting Policies - Credit Risk (Details) - Sales - Customer concentration	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Concentrations of Credit Risk
Sales to major customers (as a percent)	100.00%	100.00%	100.00%
Company A
Concentrations of Credit Risk
Sales to major customers (as a percent)	29.00%	19.00%	5.00%
Company B
Concentrations of Credit Risk
Sales to major customers (as a percent)	13.00%
Company C
Concentrations of Credit Risk
Sales to major customers (as a percent)	3.00%	13.00%	16.00%
Company D
Concentrations of Credit Risk
Sales to major customers (as a percent)	2.00%	18.00%	29.00%
Company E
Concentrations of Credit Risk
Sales to major customers (as a percent)	1.00%	9.00%	12.00%
All others
Concentrations of Credit Risk
Sales to major customers (as a percent)	52.00%	41.00%	38.00%