INVESTMENT AND MORTGAGE-BACKED SECURITIES - Sales Information and Marketable Equity Securities (Details) - USD ($)	3 Months Ended		9 Months Ended		15 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021
Sales of Available-for-sale Securities:
Proceeds			$ 138,077,000	$ 68,784,000
Proceeds:
Marketable equity securities		$ 137,000	6,101,000	410,000
Net gain on equity securities	$ 0	175,000	131,000	139,000
Sales of securities held-to-maturity			0	0	$ 0
Transfers to or from securities held-to-maturity	$ 0	0	0	0
Agency Notes
Sales of Available-for-sale Securities:
Proceeds				273,000
Corporate Securities
Sales of Available-for-sale Securities:
Proceeds			50,273,000	25,403,000
Gross gains			729,000	1,344,000
Tax expense on gain			232,000	423,000
Gross losses			41,000
Tax benefit on loss			13,000
Pass-through MBS issued by GSEs
Sales of Available-for-sale Securities:
Proceeds		5,987,000	26,823,000	39,182,000
Gross gains		215,000	187,000	2,005,000
Tax expense on gain		$ 67,000	59,000	630,000
Gross losses			35,000
Tax benefit on loss			11,000
Agency Collateralized Mortgage Obligations ("CMOs")
Sales of Available-for-sale Securities:
Proceeds			41,324,000	4,199,000
Gross gains			268,000	8,000
Tax expense on gain			85,000	$ 3,000
Gross losses			44,000
Tax benefit on loss			14,000
State and municipal obligations.
Sales of Available-for-sale Securities:
Proceeds			19,657,000
Gross gains			143,000
Tax expense on gain			$ 45,000