INVESTMENT SECURITIES - Amortized cost and fair value of securities available-for-sale (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Sep. 30, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 35,750	$ 31,602
Gross Unrealized Gains	980	688
Gross Unrealized Losses	(64)	(57)
Fair Value	36,666	32,233
U.S. Treasury debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	250	250
Gross Unrealized Gains	4
Gross Unrealized Losses		(1)
Fair Value	254	249
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,000	8,117
Gross Unrealized Gains	55	249
Gross Unrealized Losses	(11)	(10)
Fair Value	6,044	8,356
Government National Mortgage Association ("GNMA") mortgage-backed securities - residential
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	23,806	20,488
Gross Unrealized Gains	798	351
Gross Unrealized Losses		(28)
Fair Value	24,604	20,811
Federal National Mortgage Association ("FNMA") mortgage-backed securities - residential
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,616	1,102
Gross Unrealized Gains	61	53
Fair Value	1,677	1,155
Corporate collateralized mortgage obligations ("CMO") and MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,078	1,645
Gross Unrealized Gains	62	35
Gross Unrealized Losses	(53)	(18)
Fair Value	4,087	1,662
Small Business Investment Company ("SBIC")
Debt Securities, Available-for-sale [Line Items]
Payments to Acquire Investments	500
Contractual Obligation		900
Other Assets [Member] \| Small Business Investment Company ("SBIC")
Debt Securities, Available-for-sale [Line Items]
Balance with SBIC included in other assets	$ 2,100	$ 2,100

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).

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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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Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

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Sum of the carrying amounts as of the balance sheet date of all investments.

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The cash outflow associated with the purchase of all investments (debt, security, other) during the period.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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