Quarterly report pursuant to Section 13 or 15(d)

Revenue from Contracts with Customers - Additional Information (Detail)

v3.8.0.1
Revenue from Contracts with Customers - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Concentration Risk [Line Items]    
Revenue $ 33,739 $ 30,570
Revenue | Product Concentration | Turnkey Energy Conservation Projects    
Concentration Risk [Line Items]    
Concentration percentage 29.00%