Basis of Presentation and Significant Accounting Policies - Revenue Recognized from PPA Sales (Additional Information) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Unrecorded Unconditional Purchase Obligation [Line Items]
Fuel revenue	$ 100,000	$ 300,000	$ 300,000	$ 500,000
Interest revenue	400,000	500,000	800,000	1,000,000
Revenue	168,881,000	86,783,000	338,242,000	158,980,000
Service revenue
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue related to sales-type leases	900,000	1,000,000	1,800,000	2,100,000
Operating lease revenue	3,800,000	3,900,000	7,600,000	7,800,000
Revenue	19,975,000	18,875,000	39,882,000	37,466,000
Product revenue
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue related to sales-type leases	0	0	0	0
Revenue	108,654,000	39,935,000	229,961,000	67,600,000
Electricity
Unrecorded Unconditional Purchase Obligation [Line Items]
Operating lease revenue	7,700,000	7,100,000	15,400,000	14,200,000
Revenue	14,007,000	13,619,000	$ 28,036,000	27,267,000
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	5,700,000	5,800,000	$ 11,500,000	11,600,000
Service revenue | Power generation
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue	$ 3,400,000	$ 3,400,000	$ 6,900,000	$ 6,900,000