Business Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Business Segments
Total revenues	$ 18,365	$ 18,116
Segment operating income (loss)	(446)	(95)
Operating segments
Business Segments
Total revenues	18,365	18,116
Segment operating income (loss)	1,863	1,957
Operating segments | Roadway Sensors
Business Segments
Total revenues	9,905	9,020
Segment operating income (loss)	2,602	1,797
Operating segments | Transportation Systems
Business Segments
Total revenues	7,378	7,665
Segment operating income (loss)	927	854
Operating segments | Performance Analytics
Business Segments
Total revenues	1,082	1,431
Segment operating income (loss)	$ (1,666)	$ (694)