Real Estate Securities - Components of Carrying Value (Which Equals Fair Value) of Residential Available for Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Principal balance	$ 289,659		$ 304,077
Credit reserve	(43,186)		(32,940)
Unamortized discount, net	(99,221)		(124,255)
Amortized cost	147,252		146,882
Gross unrealized gains	63,455		92,481
Gross unrealized losses	(2,507)		(29)
Allowance for credit losses	(1,027)	$ (1,471)	0
Carrying Value	207,173		239,334
Senior
Debt Securities, Available-for-sale [Line Items]
Principal balance	0		26,331
Credit reserve	0		(533)
Unamortized discount, net	0		(10,427)
Amortized cost	0		15,371
Gross unrealized gains	0		10,450
Gross unrealized losses	0		(29)
Allowance for credit losses	0
Carrying Value	0		25,792
Mezzanine
Debt Securities, Available-for-sale [Line Items]
Principal balance	2,000		13,512
Credit reserve	0		0
Unamortized discount, net	0		(527)
Amortized cost	2,000		12,985
Gross unrealized gains	16		702
Gross unrealized losses	0		0
Allowance for credit losses	0
Carrying Value	2,016		13,687
Subordinate
Debt Securities, Available-for-sale [Line Items]
Principal balance	287,659		264,234
Credit reserve	(43,186)		(32,407)
Unamortized discount, net	(99,221)		(113,301)
Amortized cost	145,252		118,526
Gross unrealized gains	63,439		81,329
Gross unrealized losses	(2,507)		0
Allowance for credit losses	(1,027)
Carrying Value	$ 205,157		$ 199,855

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Debt Securities, Available For Sale, Principal Balance

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Debt Securities, Available For Sale, Unamortized Discounts Premiums

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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