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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
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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/2003/role/recommendedDisclosureRef
-Publisher FASB
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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).

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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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Mortgage-Backed Securities and other securities - Sales and realized gains (losses) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds										$ 2,430,054
Net Gain (Loss)	$ 11,992	$ 21,399	$ (8)	$ (5,105)	$ (33,995)	$ (24,229)	$ (5,608)	$ 575	$ 28,278	(63,257)	$ 20,598
Total mortgage-backed securities and other securities
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds									1,136,617		1,589,145
Gross Gains									34,669	18,512	32,632
Gross Losses									(5,814)	(81,721)	(12,034)
Net Gain (Loss)									28,855	(63,209)	20,598
Agency CMBS
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds									891,072	1,534,967
Gross Gains									32,793	0
Gross Losses									(4,190)	(51,045)
Net Gain (Loss)									28,603	(51,045)
Subtotal Agency RMBS
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds									205,310	589,854	1,251,985
Gross Gains									1,559	18	5,020
Gross Losses									0	(23,997)	(7,936)
Net Gain (Loss)									1,559	(23,979)	(2,916)
Subtotal Agency RMBS \| Agency interest only strips accounted for as derivatives
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds											2,600
Gross Gains											432
Subtotal Agency RMBS \| Non Agency RMBS Interest Only Strips Accounted For As Derivatives
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds											2,200
Gross Gains											274
Gross Losses											(180)
Non-Agency RMBS
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds										99,842	243,838
Gross Gains										7,008	24,356
Gross Losses										(478)	(2,241)
Net Gain (Loss)										6,530	22,115
Non-Agency CMBS
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds									40,235	140,292	54,875
Gross Gains									317	3,086	2,543
Gross Losses									(1,624)	(6,201)	(1,803)
Net Gain (Loss)									$ (1,307)	(3,115)	740
Other securities
Debt Securities, Available-for-sale, Gain (Loss) [Abstract]
Proceeds										65,099	38,447
Gross Gains										8,400	713
Gross Losses										0	(54)
Net Gain (Loss)										$ 8,400	$ 659