SECURITIES - Summary of amortized cost of securities available for sale and their estimated fair value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 311,683	$ 238,870
Gross Unrealized Gains	4,310	5,928
Gross Unrealized Losses	(1,847)	(211)
Estimated Fair Value	314,146	244,587
U.S. Treasury Note
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,901	9,989
Gross Unrealized Gains	0	11
Gross Unrealized Losses	(128)	0
Estimated Fair Value	6,773	10,000
Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	86,169	57,478
Gross Unrealized Gains	2,038	1,863
Gross Unrealized Losses	(89)	0
Estimated Fair Value	88,118	59,341
U.S. Government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	25,311	19,787
Gross Unrealized Gains	73	89
Gross Unrealized Losses	(144)	(201)
Estimated Fair Value	25,240	19,675
Obligations issued by U.S. states and their political subdivisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	21,106	23,280
Gross Unrealized Gains	1,161	1,515
Gross Unrealized Losses	(3)	0
Estimated Fair Value	22,264	24,795
Residential one-to-four family
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	123,930	71,773
Gross Unrealized Gains	237	951
Gross Unrealized Losses	(1,364)	(8)
Estimated Fair Value	122,803	72,716
Multifamily
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	41,497	56,563
Gross Unrealized Gains	790	1,499
Gross Unrealized Losses	(73)	(2)
Estimated Fair Value	42,214	$ 58,060
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,769
Gross Unrealized Gains	11
Gross Unrealized Losses	(46)
Estimated Fair Value	$ 6,734