Mortgage-Backed Securities - Gains and Losses from Sales of Investments (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Investment Holdings [Line Items]
Net realized gain (loss)	$ 0	$ 65,041	$ 45,313	$ 167,275
Non-Agency RMBS
Investment Holdings [Line Items]
Proceeds from sales:	0	604	47,877	142,564
Gross realized gains:	0	0	37,742	21,274
Gross realized losses:	0	(2,214)	(4,955)	(8,392)
Agency RMBS
Investment Holdings [Line Items]
Proceeds from sales:	0	0	626	5,710,134
Gross realized gains:	0	0	0	74,264
Gross realized losses:	0	0	(1,209)	(5,816)
Agency CMBS
Investment Holdings [Line Items]
Proceeds from sales:	0	734,320	201,037	1,060,987
Gross realized gains:	0	70,237	13,735	88,927
Gross realized losses:	$ 0	$ (2,982)	$ 0	$ (2,982)

Net gain (loss) resulting from the sales of securitized, pay-through debt securities collateralized by real estate mortgage loans (mortgages).

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The difference between the carrying value and the sale price of an investment. A gain would be recognized when the sale price of the investment is greater than the carrying value of the investment. This element refers to the Gain included in earnings and not to the cash proceeds of the sale.

+ References

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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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The difference between the carrying value and the sale price of an investment. A loss would be recognized when the sale price of the investment is less than the carrying value of the investment. This element refers to the Loss included in earnings and not to the cash proceeds of the sale.

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Amount of cash inflow from sale 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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