Major Customers - Narrative (Details) - Customer Concentration Risk - customer	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Sales Revenue, Services, Net
Concentration Risk [Line Items]
Concentration risk, number of customers	2	2
Sales Revenue, Services, Net | Major Customer Number One
Concentration Risk [Line Items]
Concentration risk, percentage	23.00%	16.00%
Sales Revenue, Services, Net | Major Customer Number Two
Concentration Risk [Line Items]
Concentration risk, percentage	16.00%	12.00%
Accounts Receivable | Major Customer Number One
Concentration Risk [Line Items]
Concentration risk, percentage	65.00%
Accounts Receivable | Major Customer Number Two
Concentration Risk [Line Items]
Concentration risk, percentage	1.00%