Segment Information Narrative (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue, Major Customer [Line Items]
Number of reportable segments	3	3
Concentration risk, supplier	We currently buy a majority of our integrated circuit board assemblies from three suppliers. Management believes that other suppliers could provide similar products, but a change in suppliers, disputes with our suppliers, or unexpected constraints on the suppliers' production capacity could adversely affect operating results.
Sales [Member] | Customer A [Member]
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage	11.00%
Sales [Member] | Threshold for Reporting Customer Concentration [Member]
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage		10.00%