Segment, Geographical and Other Revenue Information - Concentration Risk (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Customer Concentration Risk [Member] | Customer A [Member] | Sales [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	41.00%	48.00%
Customer Concentration Risk [Member] | Customer B [Member] | Sales [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	35.00%	24.00%
Customer Concentration Risk [Member] | Customer C [Member] | Sales [Member]
Concentration Risk [Line Items]
Concentration risk, percentage		10.00%
Credit Concentration Risk [Member] | Customer A [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	33.00%		37.00%
Credit Concentration Risk [Member] | Customer B [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	30.00%		17.00%
Credit Concentration Risk [Member] | Customer D [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	17.00%
Credit Concentration Risk [Member] | Customer E [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Concentration risk, percentage			11.00%
Credit Concentration Risk [Member] | Customer F [Member] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Concentration risk, percentage			16.00%