Basis of Presentation and Significant Accounting Policies - Estimated Depreciable Lives (Details)	9 Months Ended
	Sep. 30, 2018
Energy Servers | Minimum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	15 years
Energy Servers | Maximum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	21 years
Computers, software and hardware | Minimum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	3 years
Computers, software and hardware | Maximum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	5 years
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	5 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	10 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	3 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	5 years
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	1 year
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated depreciable life	5 years
Buildings
Property, Plant and Equipment [Line Items]
Estimated depreciable life	35 years