Mortgage-Backed Securities - Significant Credit Quality Indicators (Details)	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Investment Holdings [Line Items]
Amortized Cost	$ 2,511,659,000	$ 3,303,310,000
Non-Agency RMBS - Senior
Investment Holdings [Line Items]
Amortized Cost	$ 32,143,429	$ 46,500,000
Non-Agency RMBS - Senior \| Credit Quality Indicator, Updated Quarterly \| Weighted Average Borrowing Rates \| Discount Rate
Investment Holdings [Line Items]
Significant Inputs	0.062	0.092
Non-Agency RMBS - Senior \| Credit Quality Indicator, Updated Quarterly \| Weighted Average Borrowing Rates \| CDR
Investment Holdings [Line Items]
Significant Inputs	0.046	0.035
Non-Agency RMBS - Senior \| Credit Quality Indicator, Updated Quarterly \| Weighted Average Borrowing Rates \| Loss Severity
Investment Holdings [Line Items]
Significant Inputs	0.546	0.583
Non-Agency RMBS - Subordinated
Investment Holdings [Line Items]
Amortized Cost	$ 1,352
Non-Agency RMBS - Subordinated \| Credit Quality Indicator, Updated Quarterly \| Weighted Average Borrowing Rates \| Discount Rate
Investment Holdings [Line Items]
Significant Inputs	0.060
Non-Agency RMBS - Subordinated \| Credit Quality Indicator, Updated Quarterly \| Weighted Average Borrowing Rates \| CDR
Investment Holdings [Line Items]
Significant Inputs	0.003
Non-Agency RMBS - Subordinated \| Credit Quality Indicator, Updated Quarterly \| Weighted Average Borrowing Rates \| Loss Severity
Investment Holdings [Line Items]
Significant Inputs	0.300

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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