Business Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)
Business Segments
Number of reportable segments | segment			3
Product revenues	$ 11,702	$ 11,086	$ 23,625	$ 22,093
Service revenues	13,546	12,974	28,806	25,893
Total revenues	25,248	24,060	52,431	47,986
Segment income (loss)	(1,099)	(185)	(1,651)	(276)
Operating segments
Business Segments
Product revenues	11,702	11,086	23,625	22,093
Service revenues	13,546	12,974	28,806	25,893
Total revenues	25,248	24,060	52,431	47,986
Segment income (loss)	2,487	3,119	5,534	6,160
Operating segments | Roadway Sensors
Business Segments
Product revenues	11,150	10,833	22,430	21,437
Service revenues	111	62	111	62
Total revenues	11,261	10,895	22,541	21,499
Segment income (loss)	2,790	2,647	5,337	4,956
Operating segments | Transportation Systems
Business Segments
Product revenues	552	253	1,195	656
Service revenues	12,542	12,074	26,626	24,070
Total revenues	13,094	12,327	27,821	24,726
Segment income (loss)	1,933	2,549	4,265	4,894
Operating segments | Agriculture and Weather Analytics
Business Segments
Service revenues	893	838	2,069	1,761
Total revenues	893	838	2,069	1,761
Segment income (loss)	$ (2,236)	$ (2,077)	$ (4,068)	$ (3,690)