Fair Value Measurements - Effect of Fair Value Measured Assets and Liabilities on Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gain (loss) on derivatives	$ 6,029	$ 6,449	$ 3,712	$ 11,063
Unrealized gain (loss) on marketable securities	0	(758)	0	(1,756)
Derivative expense related to credit default swaps		271		881
Fair Value Measurements Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gain (loss) on derivatives	6,029	6,449	3,712	11,063
Unrealized gain (loss) on marketable securities	0	(758)	0	(1,756)
Realized gain (loss) on marketable securities	0	34	0	2,142
Net	6,029	(555)	3,712	1,944
Fair Value Measurements Recurring \| Interest rate derivatives - floors
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gain (loss) on derivatives	(72)	6,185	(462)	10,173
Realized gain (loss) on interest rate floors	0	(6,280)	0	(9,505)
Fair Value Measurements Recurring \| Interest rate derivatives - caps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gain (loss) on derivatives	(24)	(59)	(554)	(129)
Fair Value Measurements Recurring \| Credit default swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gain (loss) on derivatives	0	323	0	1,019
Fair Value Measurements Recurring \| Embedded debt derivative
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gain (loss) on derivatives	6,125	0	4,728	0
Fair Value Measurements Recurring \| Derivative liabilities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	6,029	(555)	3,712	1,944
Fair Value Measurements Recurring \| Derivative liabilities \| Embedded debt derivative
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	6,125	0	4,728	0
Fair Value Measurements Recurring \| Derivative assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	(96)	169	(1,016)	1,558
Fair Value Measurements Recurring \| Derivative assets \| Interest rate derivatives - floors
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	(72)	(95)	(462)	668
Fair Value Measurements Recurring \| Derivative assets \| Interest rate derivatives - caps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	(24)	(59)	(554)	(129)
Fair Value Measurements Recurring \| Derivative assets \| Credit default swaps
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0	323	0	1,019
Fair Value Measurements Recurring \| Non-derivative assets
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	(96)	(555)	(1,016)	1,944
Fair Value Measurements Recurring \| Non-derivative assets \| Equity
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	$ 0	$ (724)	$ 0	$ 386

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Fair value assets and liabilities measured on a recurring basis, gain loss included in investment income.

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Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

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Amount of unrealized gain (loss) on investment in marketable security.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

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