Segment Information and Foreign Operations - Concentration of Credit Risk (Details) - customer	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Revenues
Revenue, Major Customer [Line Items]
Number of customers representing significant share	1	1	2	1
Accounts Receivable
Revenue, Major Customer [Line Items]
Number of customers representing significant share			2		3
Landmark | Revenues
Revenue, Major Customer [Line Items]
Percentage share generated by major customers	16.00%	16.00%	14.00%	13.00%
Haisi Optoelectronics | Revenues
Revenue, Major Customer [Line Items]
Percentage share generated by major customers			10.00%
Major Customer One | Accounts Receivable
Revenue, Major Customer [Line Items]
Percentage share generated by major customers			13.00%		17.00%
Major Customer Two | Accounts Receivable
Revenue, Major Customer [Line Items]
Percentage share generated by major customers			11.00%		12.00%
Major Customer Three | Accounts Receivable
Revenue, Major Customer [Line Items]
Percentage share generated by major customers					10.00%
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	40.00%	39.00%	41.00%	36.00%