Commitments and Contingencies - Concentration of Credit Risk (Details) - customer	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Ten largest customers
Concentration of Credit Risk
Number of customers	10
Accounts Receivable | Credit Concentration Risk | Ten largest customers
Concentration of Credit Risk
Concentration Risk (as a percent)	61.00%	67.00%
Accounts Receivable | Credit Concentration Risk | Customer A
Concentration of Credit Risk
Concentration Risk (as a percent)		24.00%
Accounts Receivable | Credit Concentration Risk | Customer B
Concentration of Credit Risk
Concentration Risk (as a percent)	22.00%
Net Sales | Credit Concentration Risk | Customer A
Concentration of Credit Risk
Concentration Risk (as a percent)		21.00%	14.00%
Net Sales | Credit Concentration Risk | Customer C
Concentration of Credit Risk
Concentration Risk (as a percent)	12.00%