Fair Value of Assets and Liabilities - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Assets:
Cash and cash equivalents	$ 537,070	$ 283,524	$ 53,676
Carrying Value
Assets:
Cash and cash equivalents	537,070	283,524
Restricted cash and investments	48,377	28,329
Liabilities:
Borrowings under senior credit facility	1,549,783	1,474,437
Non-recourse debt	317,671	344,614
Fair Value
Assets:
Cash and cash equivalents	537,070	283,524
Restricted cash and investments	48,377	28,329
Liabilities:
Borrowings under senior credit facility	1,444,437	1,342,066
Non-recourse debt	317,671	344,632
Level 1 | Fair Value
Assets:
Cash and cash equivalents	537,070	283,524
Restricted cash and investments	48,377	28,329
Significant Other Observable Inputs (Level 2) | Fair Value
Liabilities:
Borrowings under senior credit facility	1,444,437	1,342,066
Non-recourse debt	317,671	344,632
5.125% Senior Notes due 2023 | Carrying Value
Liabilities:
Senior notes, fair value	259,275	281,783
5.125% Senior Notes due 2023 | Fair Value
Liabilities:
Senior notes, fair value	245,410	256,096
5.125% Senior Notes due 2023 | Significant Other Observable Inputs (Level 2) | Fair Value
Liabilities:
Senior notes, fair value	245,410	256,096
6.50% Exchangeable Senior Notes due 2026 | Carrying Value
Liabilities:
Senior notes, fair value	230,000
6.50% Exchangeable Senior Notes due 2026 | Fair Value
Liabilities:
Senior notes, fair value	238,799
6.50% Exchangeable Senior Notes due 2026 | Significant Other Observable Inputs (Level 2) | Fair Value
Liabilities:
Senior notes, fair value	238,799
5.875% Senior Notes due 2022 | Carrying Value
Liabilities:
Senior notes, fair value		193,958
5.875% Senior Notes due 2022 | Fair Value
Liabilities:
Senior notes, fair value		192,736
5.875% Senior Notes due 2022 | Significant Other Observable Inputs (Level 2) | Fair Value
Liabilities:
Senior notes, fair value		192,736
5.875% Senior Notes due 2024 | Carrying Value
Liabilities:
Senior notes, fair value	225,293	242,500
5.875% Senior Notes due 2024 | Fair Value
Liabilities:
Senior notes, fair value	191,519	202,458
5.875% Senior Notes due 2024 | Significant Other Observable Inputs (Level 2) | Fair Value
Liabilities:
Senior notes, fair value	191,519	202,458
6.00% Senior Notes due 2026 | Carrying Value
Liabilities:
Senior notes, fair value	350,000	350,000
6.00% Senior Notes due 2026 | Fair Value
Liabilities:
Senior notes, fair value	276,113	279,493
6.00% Senior Notes due 2026 | Significant Other Observable Inputs (Level 2) | Fair Value
Liabilities:
Senior notes, fair value	$ 276,113	$ 279,493