FAIR VALUE - Fair Value and Related Disclosures for Debt Securities (Details) - Agency Securities Classified as Available-for-sale [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fannie Mae/Freddie Mac [Member]
Available-for-sale securities disclosure Items [Abstract]
Available-for-sale securities, Amortized Cost Basis	$ 6,788,607	$ 7,235,571
Available-for-sale securities, Gross Unrealized Gains	72,845	87,158
Available-for-sale securities, Gross Unrealized Losses	18,088	12,640
Available-for-sale securities, Fair Value	6,843,364	7,310,089
Ginnie Mae [Member]
Available-for-sale securities disclosure Items [Abstract]
Available-for-sale securities, Amortized Cost Basis	553,736	617,430
Available-for-sale securities, Gross Unrealized Gains	8,894	10,541
Available-for-sale securities, Gross Unrealized Losses	583	508
Available-for-sale securities, Fair Value	$ 562,047	$ 627,463

Amount, before tax, of unrealized gain 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).

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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).

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Amortized cost of 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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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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Amount 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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