Supplementary Financial Information - Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
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)	(7,970)	(7,970)
Goodwill, net	15,150	17,318	17,318
Activity related to warranty reserve
Balance at beginning of fiscal year	193	181	184
Additions charged to cost of sales	382	236	134
Warranty claims	(297)	(224)	(137)
Balance at end of fiscal year	278	193	181
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)
Goodwill, net	6,936	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)
Goodwill, net		$ 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
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