Mortgage-Backed Securities - Gains and Losses from Sales of Investments (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Investment Holdings [Line Items]
Net realized gain (loss)	$ 75,854	$ 8,603
Non-Agency RMBS
Investment Holdings [Line Items]
Proceeds from sales:	33,797	4,430
Gross realized gains:	1,256	285
Gross realized losses:	0	(1,320)
Agency RMBS
Investment Holdings [Line Items]
Proceeds from sales:	5,710,134	1,482,369
Gross realized gains:	74,264	27,012
Gross realized losses:	(5,816)	(15,149)
Agency CMBS
Investment Holdings [Line Items]
Proceeds from sales:	105,017	22,482
Gross realized gains:	6,150	0
Gross realized losses:	$ 0	$ (2,225)

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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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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