INVESTMENT SECURITIES - Summary of investment securities (Details) - Short-term Investments [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized cost, as adjusted	$ 52,334	$ 51,987
Gross unrealized holding gains	10	1
Gross unrealized holding losses	1	4
Estimated fair value	52,343	51,984
Obligations of domestic governmental agencies [Member]
Amortized cost, as adjusted	52,334	51,987
Gross unrealized holding gains	10	1
Gross unrealized holding losses	1	4
Estimated fair value	$ 52,343	$ 51,984

Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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