Power Purchase Agreement Programs - Additional Information (Details)			1 Months Ended	2 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
		Jun. 14, 2019 USD ($) MW	Jun. 30, 2019 MW	Aug. 31, 2019 MW	Sep. 30, 2019 USD ($) variable_interest_entity MW	Sep. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($) variable_interest_entity MW	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Variable Interest Entity [Line Items]
Standard warranty period (years)								1 year
Number of variable interest entities | variable_interest_entity					6			6
Redeemable noncontrolling interest					$ 557,000			$ 557,000		$ 57,261,000
Sale of energy savers | MW			9.7	8	8			17.7
Revenue					$ 233,471,000	$ 190,190,000		$ 667,960,000	$ 528,432,000
Cost of revenue					(180,006,000)	(166,805,000)		$ (557,067,000)	(428,610,000)
Energy servers installed | MW								9
Debt payoff make-whole penalty								$ 5,934,000	0
Interest expense					16,900,000	18,800,000		52,800,000	68,000,000
Revenue from related parties					75,703,000	172,000		168,908,000	31,097,000
Payments to acquire equity method investments		$ 57,500,000
Possible indemnification amount								97,200,000
Possible indemnification, tax expense (benefit) amount								7,500,000
Possible indemnification, cash collateral					(77,200,000)		$ 20,000,000
Possible indemnification, increase collateral obligation					20,000,000
Tariff damages collateral								57,200,000
Forced outage event, purchase price of REC								$ 45
Payment percentage under tariff								0.70
Distributions to noncontrolling and redeemable noncontrolling interests								$ (9,363,000)	(14,192,000)
Restricted cash, noncurrent	[1]				(116,890,000)			(116,890,000)		(31,100,000)
Decrease in inventories								7,896,000	44,465,000
Decrease in property plant and equipment								20,400,000
Increase in deferred revenue and customer current liabilities								(68,180,000)	(32,203,000)
Increase in accrued other current liabilities								5,029,000	1,885,000
Commitment to redeem noncontrolling interest								(43,713,000)	0
Other accrued liabilities, current					$ 24,580,000			$ 24,580,000		31,236,000
Minimum
Variable Interest Entity [Line Items]
Term of power purchase agreements (years)					10 years			10 years
Maximum
Variable Interest Entity [Line Items]
Term of power purchase agreements (years)					21 years			21 years
PPA II
Variable Interest Entity [Line Items]
Number of megawatts available for purchase | MW		17.7
Number of megawatts available for repurchase | MW		11
Number of replacement megawatts | MW		9.8
Number of megawatts available to be upgraded | MW		27
Additional funding needed to complete upgrade								$ 92,000,000
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Restricted cash, noncurrent					$ (114,213,000)			(114,213,000)		(27,854,000)
Variable Interest Entity, Primary Beneficiary | PPA II
Variable Interest Entity [Line Items]
Repayments of debt and interest								77,700,000
Repayments of debt								(11,300,000)
Debt payoff make-whole penalty								5,900,000
Debt issuance costs written-off								1,000,000
Interest expense								100,000
Increase in cash and cash equivalents								(47,800,000)
Revenue from related parties								166,400,000
Repayments of long-term debt								(72,300,000)
Noncontrolling interest, period increase (decrease)								(55,400,000)
Increase in restricted cash								97,200,000
Restricted cash, noncurrent					(97,200,000)			(97,200,000)
Decrease in property plant and equipment					(14,600,000)			(48,300,000)
Increase in long-term restricted cash								85,900,000
Commitment to redeem noncontrolling interest								(11,700,000)
Sale Of Energy Servers
Variable Interest Entity [Line Items]
Revenue					71,500,000			159,300,000
Sale Of Energy Servers | Variable Interest Entity, Primary Beneficiary | PPA II
Variable Interest Entity [Line Items]
Increase in accrued other current liabilities								700,000
Other accrued liabilities, current					12,400,000			12,400,000
Installation Services Of Energy Servers
Variable Interest Entity [Line Items]
Revenue					$ 3,200,000			$ 7,100,000
Energy Server repurchased | MW					8			17.7
Cost of revenue					$ (21,100,000)			$ (47,400,000)
Write Off Of Energy Servers
Variable Interest Entity [Line Items]
Energy Server repurchased | MW					9			19
Cost of revenue					$ 0
Product
Variable Interest Entity [Line Items]
Revenue					182,616,000	125,690,000		$ 504,249,000	355,651,000
Cost of revenue					(94,056,000)	$ (95,357,000)		(350,008,000)	$ (246,514,000)
Repurchase Of Energy Servers | Variable Interest Entity, Primary Beneficiary | PPA II
Variable Interest Entity [Line Items]
Distributions to noncontrolling and redeemable noncontrolling interests								(43,700,000)
Energy Servers, Change In Useful Lives
Variable Interest Entity [Line Items]
Cost of revenue					$ (14,600,000)			(22,700,000)
PPA II
Variable Interest Entity [Line Items]
Repayments of debt								(144,813,000)		$ (65,114,000)
Distributions to noncontrolling and redeemable noncontrolling interests								$ (43,700,000)

[1] We have variable interest entities which represent a portion of the consolidated balances are recorded within the "Cash and cash equivalents," "Restricted cash," "Accounts receivable," "Customer financing receivable," "Prepaid expenses and other current assets," "Property and equipment, net," "Customer financing receivable, non-current," "Restricted cash, non-current," "Other long-term assets," "Accounts payable," "Accrued other current liabilities," "Deferred revenue and customer deposits," "Current portion of non-recourse debt from related parties," "Derivative liabilities, net of current portion," "Deferred revenue and customer deposits, net of current portion," "Long-term portion of non-recourse debt," and "Other long-term liabilities" financial statement line items in the Condensed Consolidated Balance Sheets (see Note 12 - Power Purchase Agreement Programs).