INVESTMENT AND MORTGAGE-BACKED SECURITIES, Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Available for sale, Amortized Cost
Within one year	$ 2,123
One to five years	116,049
Five to ten years	183,014
Beyond ten years	5,145
Pass-through MBS issued by GSEs and Agency CMO	844,283
Amortized Cost	1,150,614	$ 520,261
Available for sale, Fair Value
Within one year	2,130
One to five years	115,878
Five to ten years	182,961
Beyond ten years	4,995
Pass-through MBS issued by GSEs and Agency CMO	846,529
Total	$ 1,152,493	$ 538,861

Amortized cost 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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