The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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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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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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The difference between the book value and the sale price of options, swaps, futures, forward contracts, and other derivative instruments. This element refers to the gain (loss) included in earnings.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

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Derivative, Variation Margin Settlement

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Derivative Instruments - Gains and 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
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations									$ (9,631)	$ 10,316	$ (156,076)
Mark-to-Market									9,390	(10,381)	148,308
Total	$ 42,007	$ (47,056)	$ (71,530)	$ (27,148)	$ (54,728)	$ 24,625	$ 28,490	$ 79,582	(103,727)	77,969	3,292
Collateral already posted, aggregate fair value	$ 55,400				$ 38,000				55,400	38,000
Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations									(15,038)	4,363	(157,261)
Variation Margin Settlement									(108,169)	76,979	20,258
Return (Recovery) of Basis									3,081	(1,196)	(5,471)
Mark-to-Market									9,390	(10,381)	152,465
Contractual interest income (expense), net									7,009	8,204	(6,699)
Total									(103,727)	77,969	3,292
Interest Rate Swaps \| Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations									(4,978)	163	(150,607)
Variation Margin Settlement									(108,169)	76,979	20,258
Return (Recovery) of Basis									5,769	2,465	524
Mark-to-Market									5,140	(5,147)	148,947
Contractual interest income (expense), net									3,732	3,693	(14,606)
Total									(98,506)	78,153	4,516
Interest Sate Swaption \| Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations									(332)		(115)
Mark-to-Market									0
Total									(332)		(115)
Agency RMBS Interest-Only Strips accounted for as derivatives, included in MBS \| Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations											526
Return (Recovery) of Basis									(2,688)	(3,661)	(5,995)
Mark-to-Market									(508)	(655)	(902)
Contractual interest income (expense), net									3,277	4,511	7,438
Total									81	195	1,067
Option \| Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations									1,378	(871)	(1,453)
Mark-to-Market										300	(300)
Total									1,378	(571)	(1,753)
Futures Contracts \| Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations									(12,862)	6,112	(9,130)
Mark-to-Market									4,657	(5,285)	3,044
Total									(8,205)	827	(6,086)
Foreign Currency Forwards \| Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations											32
Mark-to-Market											35
Total											67
Total Return Swap \| Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations											(552)
Mark-to-Market											1,673
Contractual interest income (expense), net											469
Total											1,590
Credit Default Swap \| Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations									(178)	(241)	(11)
Return (Recovery) of Basis											(22)
Mark-to-Market									1,029	396
Total									851	155	(33)
TBAs \| Derivative Instruments Not Accounted as Hedges Under GAAP
Amounts recognized on the statements of operations related to the Company's derivatives
Other Settlements / Expirations									1,934	(800)	4,049
Mark-to-Market									(928)	10	(10)
Total									$ 1,006	$ (790)	$ 4,039