Business Segment Information (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 USD ($)
Business Segments
Number of reportable segments | segment	3
Product revenues	$ 11,923	$ 11,007
Service revenues	15,260	12,920
Total revenues	27,183	23,927
Segment income (loss)	(552)	(90)
Operating segments
Business Segments
Product revenues	11,923	11,007
Service revenues	15,260	12,920
Total revenues	27,183	23,927
Segment income (loss)	3,047	3,041
Operating segments | Roadway Sensors
Business Segments
Product revenues	11,280	10,604
Total revenues	11,280	10,604
Segment income (loss)	2,547	2,309
Operating segments | Transportation Systems
Business Segments
Product revenues	643	403
Service revenues	14,084	11,998
Total revenues	14,727	12,401
Segment income (loss)	2,332	2,346
Operating segments | Agriculture and Weather Analytics
Business Segments
Service revenues	1,176	922
Total revenues	1,176	922
Segment income (loss)	$ (1,832)	$ (1,614)