Indebtedness - Schedule of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Long term debt, current	$ 35,484	$ 21,529
Long term debt, Noncurrent	1,713,438	1,273,416
Total	1,748,922	1,294,945
Unused Borrowing Capacity	406	13,191
Recourse Debt
Debt Instrument [Line Items]
Long term debt, current	0	0
Long term debt, Noncurrent	247,000	247,000
Total	247,000	247,000
Unused Borrowing Capacity	406	406
Recourse Debt \| Bank line of credit
Debt Instrument [Line Items]
Long term debt, current	0	0
Long term debt, Noncurrent	247,000	247,000
Total	247,000	247,000
Unused Borrowing Capacity	$ 406	$ 406
Recourse Debt \| Bank line of credit \| Minimum
Debt Instrument [Line Items]
Interest Rate	5.45%	4.58%
Recourse Debt \| Bank line of credit \| Maximum
Debt Instrument [Line Items]
Interest Rate	5.77%	4.87%
Non Recourse Debt
Debt Instrument [Line Items]
Long term debt, current	$ 35,484	$ 21,529
Long term debt, Noncurrent	1,466,438	1,026,416
Total	1,501,922	1,047,945
Unused Borrowing Capacity	0	12,785
Non Recourse Debt \| Senior
Debt Instrument [Line Items]
Long term debt, current	19,070	3,561
Long term debt, Noncurrent	809,447	804,894
Total	828,517	808,455
Unused Borrowing Capacity	$ 0	$ 12,758
Non Recourse Debt \| Senior \| Minimum
Debt Instrument [Line Items]
Interest Rate	4.50%	3.63%
Non Recourse Debt \| Senior \| Maximum
Debt Instrument [Line Items]
Interest Rate	5.54%	4.69%
Non Recourse Debt \| Subordinated
Debt Instrument [Line Items]
Long term debt, current	$ 5,824	$ 4,301
Long term debt, Noncurrent	267,513	107,187
Total	273,337	111,488
Unused Borrowing Capacity	$ 0	$ 27
Non Recourse Debt \| Subordinated \| Minimum
Debt Instrument [Line Items]
Interest Rate	7.30%	6.36%
Non Recourse Debt \| Subordinated \| Maximum
Debt Instrument [Line Items]
Interest Rate	10.00%	7.13%
Non Recourse Debt \| Securitization Class A
Debt Instrument [Line Items]
Long term debt, current	$ 10,125	$ 3,534
Long term debt, Noncurrent	380,299	82,203
Total	390,424	85,737
Unused Borrowing Capacity	$ 0	$ 0
Interest Rate		4.40%
Non Recourse Debt \| Securitization Class A \| Minimum
Debt Instrument [Line Items]
Interest Rate	4.40%
Non Recourse Debt \| Securitization Class A \| Maximum
Debt Instrument [Line Items]
Interest Rate	5.31%
Non Recourse Debt \| Securitization Class B
Debt Instrument [Line Items]
Long term debt, current	$ 465	$ 440
Long term debt, Noncurrent	9,179	9,644
Total	9,644	10,084
Unused Borrowing Capacity	$ 0	$ 0
Interest Rate	5.38%	5.38%
Non Recourse Debt \| SREC Loans
Debt Instrument [Line Items]
Long term debt, current		$ 9,693
Long term debt, Noncurrent		22,488
Total		32,181
Unused Borrowing Capacity		$ 0
Interest Rate		7.28%

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
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Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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