FAIR VALUES OF FINANCIAL INSTRUMENTS - Fair Value and Related Disclosures for Debt Securities (Details) - Agency Securities Classified as Available-for-sale [Member] - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fannie Mae/Freddie Mac [Member]
Available-for-sale securities disclosure Items [Abstract]
Available-for-sale securities, Amortized Cost Basis	$ 7,235,571	$ 8,890,949
Available-for-sale securities, Gross Unrealized Gains	87,158	64,593
Available-for-sale securities, Gross Unrealized Losses	12,640	23,753
Available-for-sale securities, Fair Value	7,310,089	8,931,789
Ginnie Mae [Member]
Available-for-sale securities disclosure Items [Abstract]
Available-for-sale securities, Amortized Cost Basis	617,430	2,284,331
Available-for-sale securities, Gross Unrealized Gains	10,541	11,560
Available-for-sale securities, Gross Unrealized Losses	508	7,133
Available-for-sale securities, Fair Value	$ 627,463	$ 2,288,758

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
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-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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