Basis of Presentation and Significant Accounting Policies - Revenue Recognized from PPA Sales (Additional Information) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Unrecorded Unconditional Purchase Obligation [Line Items]
Fuel revenue	$ 100,000	$ 300,000	$ 400,000	$ 800,000
Interest revenue	400,000	500,000	1,100,000	1,500,000
Revenue	190,190,000	93,765,000	528,432,000	252,745,000
Service revenue
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue related to sales-type leases	800,000	1,000,000	2,600,000	3,100,000
Operating lease revenue	3,800,000	3,800,000	11,400,000	11,600,000
Revenue	20,751,000	19,511,000	60,633,000	56,977,000
Product revenue
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue related to sales-type leases	0	0	0	0
Revenue	125,690,000	45,255,000	355,651,000	112,855,000
Electricity
Unrecorded Unconditional Purchase Obligation [Line Items]
Operating lease revenue	7,800,000	7,400,000	23,200,000	21,600,000
Revenue	14,059,000	14,021,000	$ 42,095,000	41,288,000
Minimum
Unrecorded Unconditional Purchase Obligation [Line Items]
Term of PPA			10 years
Minimum | Energy Servers
Unrecorded Unconditional Purchase Obligation [Line Items]
Term during which the Company is responsible for the installation, operation and maintenance of the Energy Servers			10 years
Maximum
Unrecorded Unconditional Purchase Obligation [Line Items]
Term of PPA			21 years
Maximum | Energy Servers
Unrecorded Unconditional Purchase Obligation [Line Items]
Term during which the Company is responsible for the installation, operation and maintenance of the Energy Servers			15 years
Electricity sales | Power generation
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue	5,800,000	5,900,000	$ 17,300,000	17,500,000
Service revenue | Power generation
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue	$ 3,400,000	$ 3,500,000	$ 10,300,000	$ 10,400,000