Indebtedness - Schedule of Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long term debt, current	$ 26,937	$ 35,484
Long term debt, noncurrent	1,797,285	1,713,438
Long term debt	1,824,222	1,748,922
Unused borrowing capacity	0	406
Subordinated
Debt Instrument [Line Items]
Unused borrowing capacity	0	0
Recourse debt
Debt Instrument [Line Items]
Long term debt, current	0	0
Long term debt, noncurrent	239,035	247,000
Long term debt	239,035	247,000
Unused borrowing capacity	0	406
Recourse debt \| Bank line of credit
Debt Instrument [Line Items]
Long term debt, current	0	0
Long term debt, noncurrent	239,035	247,000
Long term debt	239,035	247,000
Unused borrowing capacity	$ 0	$ 406
Recourse debt \| Bank line of credit \| Minimum
Debt Instrument [Line Items]
Interest rate	5.59%	5.45%
Recourse debt \| Bank line of credit \| Maximum
Debt Instrument [Line Items]
Interest rate	5.90%	5.77%
Non-recourse debt
Debt Instrument [Line Items]
Long term debt, current	$ 26,937	$ 35,484
Long term debt, noncurrent	1,558,250	1,466,438
Long term debt	1,585,187	1,501,922
Unused borrowing capacity	0	0
Non-recourse debt \| Senior
Debt Instrument [Line Items]
Long term debt, current	12,679	19,070
Long term debt, noncurrent	901,108	809,447
Long term debt	913,787	828,517
Unused borrowing capacity	$ 0	$ 0
Non-recourse debt \| Senior \| Minimum
Debt Instrument [Line Items]
Interest rate	4.50%	4.50%
Non-recourse debt \| Senior \| Maximum
Debt Instrument [Line Items]
Interest rate	5.49%	5.54%
Non-recourse debt \| Subordinated
Debt Instrument [Line Items]
Long term debt, current	$ 5,715	$ 5,824
Long term debt, noncurrent	273,195	267,513
Long term debt	$ 278,910	$ 273,337
Non-recourse debt \| Subordinated \| Minimum
Debt Instrument [Line Items]
Interest rate	7.03%	7.03%
Non-recourse debt \| Subordinated \| Maximum
Debt Instrument [Line Items]
Interest rate	10.00%	10.00%
Non-recourse debt \| Securitization Class A
Debt Instrument [Line Items]
Long term debt, current	$ 8,072	$ 10,125
Long term debt, noncurrent	374,875	380,299
Long term debt	382,947	390,424
Unused borrowing capacity	$ 0	$ 0
Non-recourse debt \| Securitization Class A \| Minimum
Debt Instrument [Line Items]
Interest rate	4.40%	4.40%
Non-recourse debt \| Securitization Class A \| Maximum
Debt Instrument [Line Items]
Interest rate	5.31%	5.41%
Non-recourse debt \| Securitization Class B
Debt Instrument [Line Items]
Long term debt, current	$ 471	$ 465
Long term debt, noncurrent	9,072	9,179
Long term debt	9,543	9,644
Unused borrowing capacity	$ 0	$ 0
Interest rate	5.38%	5.38%

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))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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
-Subparagraph (SX 210.5-02.22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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-Section S99
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-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher FASB
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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.

+ References

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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