Notes payable (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Line of Credit Facility [Line Items]
Notes payable	$ 4,200	$ 14,400
Less: Notes payable - current	(2,360)	(2,360)
Notes payable - noncurrent	1,796	12,066
Value Lighting
Line of Credit Facility [Line Items]
Notes payable	2,200	2,400
TNT
Line of Credit Facility [Line Items]
Notes payable	$ 2,000	2,000
Energy Source
Line of Credit Facility [Line Items]
Notes payable		$ 10,000