Basis of Presentation and Significant Accounting Policies - Concentration of Risk (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Accounts Receivable | Customer Concentration Risk | Customer One
Concentration Risk [Line Items]
Concentration risk, percentage	58.00%		66.80%
Accounts Receivable | Customer Concentration Risk | Customer Two
Concentration Risk [Line Items]
Concentration risk, percentage	12.10%
Sales Revenue, Net | Geographic Concentration Risk | Customer One
Concentration Risk [Line Items]
Concentration risk, percentage	24.00%	17.30%
Sales Revenue, Net | Customer Concentration Risk | Customer One
Concentration Risk [Line Items]
Concentration risk, percentage	24.00%
Sales Revenue, Net | Customer Concentration Risk | Customer Two
Concentration Risk [Line Items]
Concentration risk, percentage	25.00%	53.00%
Sales Revenue, Net | Customer Concentration Risk | Customer Three
Concentration Risk [Line Items]
Concentration risk, percentage	23.00%
Sales Revenue, Net | Customer Concentration Risk | Customer Four
Concentration Risk [Line Items]
Concentration risk, percentage		17.00%