Supplementary Financial Information - Goodwill (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Activity related to carrying value of goodwill
Balance at the end of the year	$ 25,288	$ 25,288	$ 25,288
Goodwill, net	15,150	15,150	15,150
Accumulated impairment losses	(10,138)	(10,138)	(10,138)
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
Goodwill, net	6,936	6,936	6,936
Accumulated impairment losses	(7,970)	(7,970)	(7,970)
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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