Business Segments, Significant Customer and Geographic Information - Business Segments (Details)	12 Months Ended
	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Business Segments
Number of reportable segments | segment	3
Total revenues	$ 114,117,000	$ 99,123,000	$ 103,729,000
Depreciation	848,000	854,000	819,000
Segment income (loss)	(5,976,000)	(7,959,000)	(5,602,000)
Product
Business Segments
Total revenues	55,007,000	48,227,000	46,464,000
Service
Business Segments
Total revenues	59,110,000	50,896,000	57,265,000
Operating segments
Business Segments
Total revenues	114,117,000	99,123,000	103,729,000
Depreciation	607,000	531,000	534,000
Segment income (loss)	14,491,000	7,894,000	9,416,000
Operating segments | Product
Business Segments
Total revenues	55,007,000	48,227,000	46,464,000
Operating segments | Service
Business Segments
Total revenues	59,110,000	50,896,000	57,265,000
Operating segments | Roadway Sensors
Business Segments
Total revenues	49,370,000	43,492,000	44,357,000
Depreciation	200,000	233,000	221,000
Segment income (loss)	7,787,000	7,011,000	8,825,000
Operating segments | Roadway Sensors | Product
Business Segments
Total revenues	49,082,000	43,253,000	44,163,000
Operating segments | Roadway Sensors | Service
Business Segments
Total revenues	288,000	239,000	194,000
Operating segments | Transportation Systems
Business Segments
Total revenues	58,033,000	49,815,000	54,481,000
Depreciation	330,000	195,000	204,000
Segment income (loss)	10,556,000	5,907,000	8,639,000
Operating segments | Transportation Systems | Product
Business Segments
Total revenues	5,925,000	4,974,000	2,301,000
Operating segments | Transportation Systems | Service
Business Segments
Total revenues	52,108,000	44,841,000	52,180,000
Operating segments | Agriculture and Weather Analytics
Business Segments
Total revenues	6,714,000	5,816,000	4,891,000
Depreciation	77,000	103,000	109,000
Segment income (loss)	(3,852,000)	(5,024,000)	(8,048,000)
Operating segments | Agriculture and Weather Analytics | Service
Business Segments
Total revenues	$ 6,714,000	$ 5,816,000	$ 4,891,000