Segment Information - Accounts Receivable (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Customer D [Domain] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Entity-Wide Revenue, Major Customer, Percentage			15.30%		18.70%
Customer C [Domain]
Concentration Risk [Line Items]
Entity-Wide Revenue, Major Customer, Percentage		13.70%	10.90%	10.90%
Customer C [Domain] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Entity-Wide Revenue, Major Customer, Percentage			11.20%		14.50%
Customer B [Domain]
Concentration Risk [Line Items]
Entity-Wide Revenue, Major Customer, Percentage	30.10%	25.90%	35.60%	20.30%
Customer B [Domain] | Accounts Receivable [Member]
Concentration Risk [Line Items]
Entity-Wide Revenue, Major Customer, Percentage			27.30%		19.10%
Customer A [Domain]
Concentration Risk [Line Items]
Entity-Wide Revenue, Major Customer, Percentage		21.80%		31.90%