Major Customers - Narrative (Details) - Customer Concentration Risk - customer	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues
Concentration Risk [Line Items]
Number of customers	3	2
Revenues | Customer No. 1
Concentration Risk [Line Items]
Concentration risk percentage	28.00%	24.00%
Revenues | Customer No. 2
Concentration Risk [Line Items]
Concentration risk percentage	21.00%	23.00%
Revenues | Customer No. 3
Concentration Risk [Line Items]
Concentration risk percentage	10.00%
Accounts Receivable
Concentration Risk [Line Items]
Number of customers	3
Accounts Receivable | Customer No. 1
Concentration Risk [Line Items]
Concentration risk percentage	48.00%
Accounts Receivable | Customer No. 2
Concentration Risk [Line Items]
Concentration risk percentage	15.00%
Accounts Receivable | Customer No. 3
Concentration Risk [Line Items]
Concentration risk percentage	11.00%