Quarterly report pursuant to Section 13 or 15(d)

Indebtedness - Additional Information (Details)

v3.10.0.1
Indebtedness - Additional Information (Details) - USD ($)
9 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Loan outstanding balance $ 1,564,598,000 $ 1,294,945,000
Recourse debt    
Debt Instrument [Line Items]    
Loan outstanding balance 247,000,000 247,000,000
Non-recourse debt    
Debt Instrument [Line Items]    
Loan outstanding balance 1,317,598,000 1,047,945,000
Non-recourse debt | Aggregation facility, March 2023    
Debt Instrument [Line Items]    
Loan outstanding balance 511,900,000  
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 $ 30,000,000  
Interest coverage ratio 300.00%  
Loan outstanding balance $ 247,000,000 247,000,000
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 | 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 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 285,700,000  
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 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 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 188,300,000  
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 | 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 | 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%  
Senior debt | Non-recourse debt    
Debt Instrument [Line Items]    
Loan outstanding balance $ 1,067,947,000 808,455,000
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%  
Bank term loan due September 2020 | Non-recourse debt | Revolving loan facility, September 2020    
Debt Instrument [Line Items]    
Loan outstanding balance $ 189,600,000  
Subordinated debt | Non-recourse debt    
Debt Instrument [Line Items]    
Loan outstanding balance $ 157,943,000 111,488,000
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 $ 21,800,000  
Bank term loans due September 2022, Tranche One | Non-recourse debt    
Debt Instrument [Line Items]    
Basis spread on variable rate 3.00%  
Loan outstanding balance $ 11,100,000  
Bank term loans due September 2022, Tranche Two | Non-recourse debt    
Debt Instrument [Line Items]    
Basis spread on variable rate 2.25%  
Loan outstanding balance $ 17,500,000  
Securitization loans    
Debt Instrument [Line Items]    
Secured borrowings assets carrying amount 166,500,000 $ 172,800,000
Securitization loans | Non-recourse debt    
Debt Instrument [Line Items]    
Loan outstanding balance $ 91,700,000