Supplementary Financial Information - Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Activity related to carrying value of goodwill
Balance at the end of the year	$ 25,288	$ 25,288	$ 25,288
Accumulated impairment losses	(10,138)	(10,138)	(10,138)
Acquired goodwill (see Note 11)	5,440
Goodwill, net	20,590	15,150	15,150
Roadway Sensors
Activity related to carrying value of goodwill
Balance at the end of the year	8,214	8,214	8,214
Goodwill, net	8,214	8,214	8,214
Transportation Systems
Activity related to carrying value of goodwill
Balance at the end of the year	14,906	14,906	14,906
Accumulated impairment losses	(7,970)	(7,970)	(7,970)
Acquired goodwill (see Note 11)	5,440
Goodwill, net	12,376	6,936	6,936
Agriculture and Weather Analytics
Activity related to carrying value of goodwill
Balance at the end of the year	2,168	2,168	2,168
Accumulated impairment losses	$ (2,168)	$ (2,168)	$ (2,168)

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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