Business Segment Information - Reportable segments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) segment	Dec. 31, 2014 USD ($)
Business Segments
Number of reportable segments | segment			3
Revenues	$ 19,014	$ 17,540	$ 57,952	$ 54,206
Segment operating income (loss)	(1,134)	(593)	(2,148)	(1,008)
Operating segments
Business Segments
Revenues	19,014	17,540	57,952	54,206
Segment operating income (loss)	776	979	3,727	4,830
Operating segments | Roadway Sensors
Business Segments
Revenues	9,771	8,112	31,235	27,328
Segment operating income (loss)	1,672	1,053	6,562	4,972
Operating segments | Transportation Systems
Business Segments
Revenues	7,796	7,796	23,283	22,745
Segment operating income (loss)	1,017	1,381	3,101	3,202
Operating segments | Performance Analytics
Business Segments
Revenues	1,447	1,632	3,434	4,133
Segment operating income (loss)	$ (1,913)	$ (1,455)	$ (5,936)	$ (3,344)