INVESTMENT SECURITIES (Schedule of Securities with Unrealized Losses) (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) item	Dec. 31, 2020 USD ($) item
Available-for-sale Securities
Less than 12 Months, Estimated Fair Value		$ 37,916
Less than 12 Months, Unrealized/Unrecognized Losses		(81)
Total, Estimated Fair Value		37,916
Total, Unrealized/Unrecognized Losses		$ (81)
Number of securities of one issuer | item	0	0
Impairment loss	$ 0	$ 0
Available-for-sale Securities.
Available-for-sale Securities
Less than 12 Months, Estimated Fair Value	385,899	83,964
Less than 12 Months, Unrealized/Unrecognized Losses	(4,909)	(248)
12 months or more, Estimated Fair Value	28,064	385
12 months or more, Unrealized/Unrecognized Losses	(312)	(1)
Total, Estimated Fair Value	413,963	84,349
Total, Unrealized/Unrecognized Losses	(5,221)	(249)
Residential mortgage securities | Available-for-sale Securities.
Available-for-sale Securities
Less than 12 Months, Estimated Fair Value	315,184	33,734
Less than 12 Months, Unrealized/Unrecognized Losses	(3,859)	(74)
Total, Estimated Fair Value	315,184	33,734
Total, Unrealized/Unrecognized Losses	(3,859)	(74)
Commercial mortgage securities | Available-for-sale Securities.
Available-for-sale Securities
Less than 12 Months, Estimated Fair Value	14,919	12,314
Less than 12 Months, Unrealized/Unrecognized Losses	(263)	(93)
12 months or more, Estimated Fair Value	379	385
12 months or more, Unrealized/Unrecognized Losses		(1)
Total, Estimated Fair Value	15,298	12,699
Total, Unrealized/Unrecognized Losses	(263)	$ (94)
Asset-backed Securities | Available-for-sale Securities.
Available-for-sale Securities
Less than 12 Months, Estimated Fair Value	4,733
Less than 12 Months, Unrealized/Unrecognized Losses	(17)
Total, Estimated Fair Value	4,733
Total, Unrealized/Unrecognized Losses	(17)
U.S. Government agency securities | Available-for-sale Securities.
Available-for-sale Securities
Less than 12 Months, Estimated Fair Value	39,546
Less than 12 Months, Unrealized/Unrecognized Losses	(451)
12 months or more, Estimated Fair Value	27,685
12 months or more, Unrealized/Unrecognized Losses	(312)
Total, Estimated Fair Value	67,231
Total, Unrealized/Unrecognized Losses	(763)
Securities issued by states and political subdivisions in the U.S | Available-for-sale Securities.
Available-for-sale Securities
Less than 12 Months, Estimated Fair Value	11,517
Less than 12 Months, Unrealized/Unrecognized Losses	(319)
Total, Estimated Fair Value	11,517
Total, Unrealized/Unrecognized Losses	$ (319)