Segment Information and Foreign Operations - Concentration of Credit Risk (Details) - customer	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenues
Revenue, Major Customer [Line Items]
Number of customers representing significant share	0	2	2	2
Percentage share generated by major customers	10.00%
Accounts Receivable
Revenue, Major Customer [Line Items]
Number of customers representing significant share			1		1
Landmark [Member] | Revenues
Revenue, Major Customer [Line Items]
Percentage share generated by major customers		11.00%	10.00%	10.00%
Osram Opto [Member] | Revenues
Revenue, Major Customer [Line Items]
Percentage share generated by major customers		12.00%	11.00%	11.00%
Major Customer One | Accounts Receivable
Revenue, Major Customer [Line Items]
Percentage share generated by major customers			11.00%		12.00%
Top Five Major Customers | Revenues
Revenue, Major Customer [Line Items]
Number of customers representing significant share	5	5	5	5
Percentage share generated by major customers	33.00%	37.00%	35.00%	36.00%