REVENUE - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									$ 62,092
Revenue accounted for under other guidance									3,662
Total revenue	$ 22,443	$ 16,291	$ 13,198	$ 13,822	$ 15,057	$ 17,263	$ 15,422	$ 12,558	65,754	$ 60,300	$ 70,211
Product revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									52,599
Revenue accounted for under other guidance									3,662
Total revenue									56,261	55,595	66,224
Service revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									9,493
Revenue accounted for under other guidance									0
Total revenue									9,493	$ 4,705	$ 3,987
Federal government
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									3,221
Federal government | Product revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									2,579
Federal government | Service revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									642
Commercial and industrial
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									58,814
Commercial and industrial | Product revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									49,963
Commercial and industrial | Service revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									8,851
Total lighting
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									62,035
Total lighting | Product revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									52,542
Total lighting | Service revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									9,493
Solar energy related revenues
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									57
Solar energy related revenues | Product revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									57
Solar energy related revenues | Service revenue
Disaggregation Of Revenue [Line Items]
Total revenues from contracts with customers									$ 0