Business Segment Information - Business segments (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2016 USD ($) segment	Jun. 30, 2015 USD ($)
Business Segments
Number of reportable segments | segment	3
Revenues	$ 23,927	$ 18,365
Segment operating income (loss)	(90)	(446)
Operating segments
Business Segments
Revenues	23,927	18,365
Segment operating income (loss)	3,041	2,283
Operating segments | Roadway Sensors
Business Segments
Revenues	10,604	9,905
Segment operating income (loss)	2,309	2,740
Operating segments | Transportation Systems
Business Segments
Revenues	12,401	7,794
Segment operating income (loss)	2,346	851
Operating segments | Agriculture And Weather Analytics
Business Segments
Revenues	922	666
Segment operating income (loss)	$ (1,614)	$ (1,308)