Basis of Presentation and Significant Accounting Policies - Revenue Recognized from PPA Sales (Additional Information) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrecorded Unconditional Purchase Obligation [Line Items]
Fuel revenue									$ 500,000	$ 1,000,000	$ 1,900,000
Interest revenue									1,400,000	1,900,000	1,800,000
Revenue:	$ 213,606,000	$ 190,190,000	$ 168,881,000	$ 169,361,000	$ 123,251,000	$ 93,765,000	$ 86,783,000	$ 72,197,000	742,038,000	375,996,000	208,540,000
Service revenue
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue related to sales-type leases									3,400,000	4,000,000	6,700,000
Operating lease revenue									15,200,000	15,600,000	10,800,000
Revenue:	21,752,000	20,751,000	19,975,000	19,907,000	19,927,000	19,511,000	18,875,000	18,591,000	82,385,000	76,904,000	67,622,000
Product revenue
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue related to sales-type leases									0	0	0
Revenue:	156,671,000	125,690,000	108,654,000	121,307,000	66,913,000	45,255,000	39,935,000	27,665,000	512,322,000	179,768,000	76,478,000
Electricity
Unrecorded Unconditional Purchase Obligation [Line Items]
Operating lease revenue									30,900,000	29,900,000	21,200,000
Revenue:	$ 13,820,000	$ 14,059,000	$ 14,007,000	$ 14,029,000	$ 14,810,000	$ 14,021,000	$ 13,619,000	$ 13,648,000	$ 55,915,000	56,098,000	47,856,000
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:									$ 23,000,000	23,300,000	23,000,000
Service revenue | Power generation
Unrecorded Unconditional Purchase Obligation [Line Items]
Revenue:									$ 13,700,000	$ 13,900,000	$ 13,700,000