Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) - shares shares in Thousands		3 Months Ended			6 Months Ended	9 Months Ended		12 Months Ended
	Apr. 01, 2016	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Concentration Risk [Line Items]
Securities excluded from net loss per share calculation (in shares)		62	28			90	72
Warranty service periods	10 years
Minimum
Concentration Risk [Line Items]
Warranty service periods						1 year
Maximum
Concentration Risk [Line Items]
Warranty service periods						5 years
Geographic concentration risk | United States
Concentration Risk [Line Items]
Concentration risk (less than for one percent)					98.00%	97.00%
Revenue | Geographic concentration risk | Countries outside of the United States
Concentration Risk [Line Items]
Concentration risk (less than for one percent)		1.00%	1.00%	1.00%		2.00%	1.00%
Commercial Lighting Retrofit Company | Revenue | Customer concentration risk
Concentration Risk [Line Items]
Concentration risk (less than for one percent)		15.00%	23.00%			10.00%	12.00%
Commercial Lighting Retrofit Company | Accounts receivable | Customer concentration risk
Concentration Risk [Line Items]
Concentration risk (less than for one percent)						14.00%		17.00%
U.S. Navy | Revenue | Customer concentration risk
Concentration Risk [Line Items]
Concentration risk (less than for one percent)		53.00%	20.00%			45.00%	18.00%
Distributor To The U.S. Navy [Member] | Revenue | Customer concentration risk
Concentration Risk [Line Items]
Concentration risk (less than for one percent)		48.00%	12.00%			41.00%
Distributor To The U.S. Navy [Member] | Accounts receivable | Customer concentration risk
Concentration Risk [Line Items]
Concentration risk (less than for one percent)						42.00%		39.00%
Global Healthcare Systems, Northeast Ohio [Member] | Revenue | Customer concentration risk
Concentration Risk [Line Items]
Concentration risk (less than for one percent)			23.00%				17.00%
Global Healthcare Systems, Northeast Ohio [Member] | Accounts receivable | Customer concentration risk
Concentration Risk [Line Items]
Concentration risk (less than for one percent)								21.00%