Fair Value - Estimated Fair Values and Carrying Values for Customer Receivables and Debt Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jul. 01, 2017	Dec. 31, 2016	Sep. 30, 2016	Jul. 31, 2014	Mar. 31, 2013	Dec. 31, 2012
Senior secured notes | Senior Secured Notes due March 2025, Non-Recourse | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	$ 81,400	$ 89,564
Senior secured notes | Senior Secured Notes due March 2025, Non-Recourse | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	84,314	95,114
Senior secured notes | Senior Secured Notes due March 2030, Non-Recourse | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	82,837	84,032
Senior secured notes | Senior Secured Notes due March 2030, Non-Recourse | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	88,291	93,264
Term loan | Term Loan due September 2028, Non-Recourse | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	36,502	36,940
Term loan | Term Loan due September 2028, Non-Recourse | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	42,927	46,713
Term loan | Senior Secured Notes due October 2020, Non-Recourse | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	24,021	24,364
Term loan | Senior Secured Notes due October 2020, Non-Recourse | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	26,562	27,206
Term loan | Term Loan due December 2021, Non-Recourse | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	123,834	125,596
Term loan | Term Loan due December 2021, Non-Recourse | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	130,033	131,817
Term loan | Term Loan due November 2020, Recourse | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	3,631	4,887
Term loan | Term Loan due November 2020, Recourse | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	4,265	5,148
Convertible promissory notes | Convertible Promissory Notes due December 2019 and 2020, Recourse | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	34,273	0
Convertible promissory notes | Convertible Promissory Notes due December 2019 and 2020, Recourse | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	40,548	0
Convertible promissory notes | Convertible Promissory Notes One due December 2020 | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	258,862	236,724
Convertible promissory notes | Convertible Promissory Notes One due December 2020 | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	919,260	219,094
Notes | Notes due July 2024, Recourse | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	95,451	94,517
Notes | Notes due July 2024, Recourse | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	102,162	106,124
Customer financing receivables | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer financing receivables	74,030	77,885
Customer financing receivables | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer financing receivables	52,037	55,255
Affiliated entity | Convertible promissory notes | Convertible Promissory Notes due December 2019 and 2020, Recourse | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	0	244,717
Affiliated entity | Convertible promissory notes | Convertible Promissory Notes due December 2019 and 2020, Recourse | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument	$ 0	$ 211,000
Convertible Promissory Notes Interest Rate 8% Due December 2019 And 2020, Recourse | Affiliated entity
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate percentage		8.00%
Convertible Promissory Notes due December 2020, Recourse | Convertible promissory notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate percentage	6.00%	6.00%		6.00%
Convertible Promissory Notes due December 2020, Recourse | Affiliated entity | Convertible promissory notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate percentage				6.00%	6.00%	5.00%
Notes due July 2024, Recourse
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate percentage	10.00%	10.00%
Notes due July 2024, Recourse | Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate percentage			10.00%
PPA Company II | Senior Secured Notes due March 2025, Non-Recourse | Senior secured notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate percentage	5.22%	5.20%						5.22%
PPA Company IIIa | Term Loan due September 2028, Non-Recourse | Term loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate percentage	7.50%	7.50%							7.50%
PPA Company IV | Senior Secured Notes due March 2030, Non-Recourse | Senior secured notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate percentage	6.07%	6.10%					6.07%