Investment Securities Available for Sale, at Fair Value - Proceeds from Sale (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Sales Proceeds	$ 1,383,390
Sales Proceeds	1,380,980	$ 56,769
Realized Gains	11,058	16,957
Realized Losses	(69,795)	(156)
Net Realized Gains/Losses	(58,737)	16,801
Agency RMBS
Debt Securities, Available-for-sale [Line Items]
Sales Proceeds	992,993
Realized Gains	5,392
Realized Losses	(15,870)
Net Realized Gains/Losses	(10,478)
Agency RMBS \| Agency ARMs
Debt Securities, Available-for-sale [Line Items]
Sales Proceeds	49,893
Realized Gains	44
Realized Losses	(4,157)
Net Realized Gains/Losses	(4,113)
Agency RMBS \| Agency Fixed- Rate
Debt Securities, Available-for-sale [Line Items]
Sales Proceeds	943,100
Realized Gains	5,348
Realized Losses	(11,713)
Net Realized Gains/Losses	(6,365)
Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Sales Proceeds	145,411
Realized Gains	5,666
Realized Losses	(209)
Net Realized Gains/Losses	5,457
Total Agency
Debt Securities, Available-for-sale [Line Items]
Sales Proceeds	1,138,404
Realized Gains	11,058
Realized Losses	(16,079)
Net Realized Gains/Losses	(5,021)
Non-Agency RMBS
Debt Securities, Available-for-sale [Line Items]
Sales Proceeds	130,948
Realized Gains	0
Realized Losses	(24,132)
Net Realized Gains/Losses	(24,132)
CMBS
Debt Securities, Available-for-sale [Line Items]
Sales Proceeds	114,038
Sales Proceeds		56,769
Realized Gains	0	16,957
Realized Losses	(29,584)	(156)
Net Realized Gains/Losses	$ (29,584)	$ 16,801

Proceeds Including Receivable For Unsettled Trades From Sale of Debt Securities, Available-for-sale

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563

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

+ References

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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).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 320
-SubTopic 10
-Section 45
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
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+ References

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