Indebtedness - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Loan outstanding balance	$ 1,824,222,000	$ 1,748,922,000
Recourse debt
Debt Instrument [Line Items]
Loan outstanding balance	239,035,000	247,000,000
Non-recourse debt
Debt Instrument [Line Items]
Loan outstanding balance	1,585,187,000	1,501,922,000
Non-recourse debt | Aggregation facility, March 2023
Debt Instrument [Line Items]
Loan outstanding balance	362,600,000
Non-recourse debt | Line of credit | Aggregation facility, March 2023
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	$ 595,000,000
Non-recourse debt | London Interbank Offered Rate (LIBOR) | Line of credit | Aggregation facility, March 2023
Debt Instrument [Line Items]
Basis spread on variable rate	2.50%
Facility available period	3 years
Debt instrument basis spread on variable rate, periodic increase	2.75%
Revolving line of credit facility available period, period increase	2 years
Bank line of credit | Recourse debt
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	$ 250,000,000
Minimum unencumbered liquid assets to be maintained	25,000,000
Debt covenant, liability maintenance	$ 30,000,000
Interest coverage ratio	300.00%
Loan outstanding balance	$ 239,035,000	$ 247,000,000
Bank line of credit | Recourse debt | Minimum
Debt Instrument [Line Items]
Interest rate	5.59%	5.45%
Bank line of credit | Recourse debt | Maximum
Debt Instrument [Line Items]
Interest rate	5.90%	5.77%
Bank line of credit | Recourse debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	3.25%
Bank line of credit | Recourse debt | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	2.25%
Bank line of credit | Recourse debt | Federal Funds Rate
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
Bank line of credit | Recourse debt | LIBOR Floor Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Term Loan Due in October 2024 | Non-recourse debt | Senior secured revolving letter of credit facility | Aggregation facility, October 2024
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	$ 303,000,000
Loan outstanding balance	281,800,000
Term Loan Due in October 2024 | Non-recourse debt | Term Loan | Aggregation facility, October 2024
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	293,000,000
Term Loan Due in October 2024 | Non-recourse debt | Revolving debt | Aggregation facility, October 2024
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	$ 10,000,000
Term Loan | Non-recourse debt | Minimum | Aggregation facility, March 2023
Debt Instrument [Line Items]
Term loan prepayment penalty, percent	0.00%
Term Loan | Non-recourse debt | Maximum | Aggregation facility, March 2023
Debt Instrument [Line Items]
Term loan prepayment penalty, percent	1.00%
Term Loan | Non-recourse debt | London Interbank Offered Rate (LIBOR) | Aggregation facility, March 2023
Debt Instrument [Line Items]
Basis spread on variable rate	5.00%
Facility available period	3 years
Debt instrument basis spread on variable rate, periodic increase	6.50%
Term Loan A | Non-recourse debt | London Interbank Offered Rate (LIBOR) | Aggregation facility, October 2024
Debt Instrument [Line Items]
Basis spread on variable rate	2.75%
Term Loan A | Non-recourse debt | Base Rate | Aggregation facility, October 2024
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%
Term Loan B | Non-recourse debt | Minimum | Aggregation facility, October 2024
Debt Instrument [Line Items]
Term loan prepayment penalty, percent	0.00%
Term Loan B | Non-recourse debt | Maximum | Aggregation facility, October 2024
Debt Instrument [Line Items]
Term loan prepayment penalty, percent	5.00%
Term Loan B, Class A | Non-recourse debt | London Interbank Offered Rate (LIBOR) | Aggregation facility, October 2024
Debt Instrument [Line Items]
Basis spread on variable rate	7.03%
Term Loan B, Class B | Non-recourse debt | London Interbank Offered Rate (LIBOR) | Aggregation facility, October 2024
Debt Instrument [Line Items]
Basis spread on variable rate	5.00%
Basis spread on Federal Funds Rate	1.00%
Term Loan B, Class B | Non-recourse debt | Base Rate | Aggregation facility, October 2024
Debt Instrument [Line Items]
Basis spread on variable rate	4.00%
Basis spread on Federal Funds Rate	0.50%
Term Loan due in April 2024 | Non-recourse debt | Senior secured revolving letter of credit facility | Aggregation facility, April 2024
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	$ 202,000,000
Loan outstanding balance	183,800,000
Term Loan due in April 2024 | Non-recourse debt | Revolving debt | Aggregation facility, April 2024
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	7,000,000
Term Loan due in April 2024 | Non-recourse debt | Delayed draw term loan | Aggregation facility, April 2024
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	$ 195,000,000
Term Loan due in April 2024 | Non-recourse debt | London Interbank Offered Rate (LIBOR) | Aggregation facility, April 2024
Debt Instrument [Line Items]
Basis spread on variable rate	2.25%
Facility available period	4 years
Term Loan due in April 2024 | Non-recourse debt | Base Rate | Aggregation facility, April 2024
Debt Instrument [Line Items]
Basis spread on variable rate	1.25%
Term Loan due in April 2024 | Non-recourse debt | Federal Funds Rate | Aggregation facility, April 2024
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
Term Loan due in April 2024 | Non-recourse debt | LIBOR Floor Rate | Aggregation facility, April 2024
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Bank Term Loan due September 2020 | Non-recourse debt | Revolving loan facility, September 2020
Debt Instrument [Line Items]
Loan outstanding balance	$ 210,200,000
Senior debt | Non-recourse debt
Debt Instrument [Line Items]
Loan outstanding balance	$ 913,787,000	$ 828,517,000
Senior debt | Non-recourse debt | Minimum
Debt Instrument [Line Items]
Interest rate	4.50%	4.50%
Senior debt | Non-recourse debt | Maximum
Debt Instrument [Line Items]
Interest rate	5.49%	5.54%
Senior debt | Non-recourse debt | London Interbank Offered Rate (LIBOR) | Revolving loan facility, September 2020
Debt Instrument [Line Items]
Basis spread on variable rate	2.75%
Subordinated debt | Non-recourse debt
Debt Instrument [Line Items]
Loan outstanding balance	$ 278,910,000	$ 273,337,000
Subordinated debt | Non-recourse debt | Minimum
Debt Instrument [Line Items]
Interest rate	7.03%	7.03%
Subordinated debt | Non-recourse debt | Maximum
Debt Instrument [Line Items]
Interest rate	10.00%	10.00%
Subordinated debt | Non-recourse debt | London Interbank Offered Rate (LIBOR) | Revolving loan facility, September 2020
Debt Instrument [Line Items]
Basis spread on variable rate	5.50%
Bank Term Loan due April 2022 | Non-recourse debt
Debt Instrument [Line Items]
Loan outstanding balance	$ 20,000,000
Interest rate	4.50%
Bank Term Loan due September 2022 | Non-recourse debt
Debt Instrument [Line Items]
Basis spread on variable rate	2.25%
Loan outstanding balance	$ 16,100,000
Bank Term Loan due January 2030 | Non-recourse debt
Debt Instrument [Line Items]
Loan outstanding balance	$ 118,200,000
Interest rate	10.00%
Subsidiary one | Securitization loans
Debt Instrument [Line Items]
Secured borrowings assets carrying amount	$ 162,700,000	$ 164,700,000
Subsidiary one | Securitization loans | Non-recourse debt
Debt Instrument [Line Items]
Loan outstanding balance	$ 89,100,000
Subsidiary one | Solar Asset Backed Notes
Debt Instrument [Line Items]
Debt Instrument Discount Rate	0.08%
Subsidiary two | Securitization loans | Non-recourse debt
Debt Instrument [Line Items]
Loan outstanding balance	$ 303,400,000
Subsidiary two | Solar Asset Backed Notes
Debt Instrument [Line Items]
Debt Instrument Discount Rate	1.47%