Segment Information Narrative (Details)	9 Months Ended
Sep. 30, 2018
Segment Reporting [Abstract]
Number of reportable segments	4
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.

Description of risks that arise due to the volume of business transacted with a particular supplier or reliance placed on that supplier. At a minimum, the description informs financial statement users of the general nature of the risk.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=99380358&loc=d3e7102-108593

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6327-108592

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Balance Type:	na
Period Type:	duration