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SECURITIES - Unrealized Loss Position (Details) $ in Thousands | Mar. 31, 2021 USD ($) security | Dec. 31, 2020 USD ($) security
--- | --- | ---
Unrealized Loss Position For: |  |
Estimated Fair Value | $ 71,849,437 | $ 75,652,396
Gross Unrealized Losses | (580,563) | (166,947)
Agency Mortgage-Backed Securities |  |
Unrealized Loss Position For: |  |
Estimated Fair Value | 18,862,476 | 777,586
Gross Unrealized Losses | $ (439,060) | $ (2,030)
Number of Securities | security | 381 | 30
Agency Mortgage-Backed Securities | Available For Sale Securities, Continuous Unrealized Loss Positions, Less Than 12 Months |  |
Unrealized Loss Position For: |  |
Estimated Fair Value | $ 18,862,476 | $ 777,586
Gross Unrealized Losses | $ (439,060) | $ (2,030)
Number of Securities | security | 381 | 30
Agency Mortgage-Backed Securities | Available For Sale Securities, Continuous Unrealized Loss Positions, Greater Than 12 Months |  |
Unrealized Loss Position For: |  |
Estimated Fair Value | $ 0 | $ 0
Gross Unrealized Losses | $ 0 | $ 0
Number of Securities | security | 0 | 0

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- Definition Mortgage-Backed Securities in a continuous unrealized loss position [Line Items] + References No definition available. + Details
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- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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- Definition Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922888-210455 + Details
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