FAIR VALUE MEASUREMENTS, Assets and Liabilities Measured at Fair Value (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	$ 617,110,000	$ 435,080,000
Assets Recorded at Fair Value on a Non-Recurring Basis [Abstract]
Mortgage servicing rights	1,380,000	1,242,000
Recurring [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	617,110,000	435,080,000
Transfers between Levels [Abstract]
Transfers from Level 1 to Level 2	0
Transfers from Level 2 to Level 1	0
Liabilities Recorded at Fair Value [Abstract]
Liabilities	0	0
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	78,610,000	38,891,000
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	538,500,000	396,189,000
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
Non-recurring [Member]
Assets Recorded at Fair Value on a Non-Recurring Basis [Abstract]
Impaired loans	4,180,000	5,700,000
Mortgage servicing rights	1,380,000	1,242,000
Total assets at fair value	5,560,000	6,942,000
Liabilities Recorded at Fair Value [Abstract]
Liabilities	0	0
Non-recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets Recorded at Fair Value on a Non-Recurring Basis [Abstract]
Impaired loans	0	0
Mortgage servicing rights	0	0
Total assets at fair value	0	0
Non-recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets Recorded at Fair Value on a Non-Recurring Basis [Abstract]
Impaired loans	0	0
Mortgage servicing rights	0	0
Total assets at fair value	0	0
Non-recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets Recorded at Fair Value on a Non-Recurring Basis [Abstract]
Impaired loans	4,180,000	5,700,000
Mortgage servicing rights	1,380,000	1,242,000
Total assets at fair value	5,560,000	6,942,000
U.S. Treasury Securities [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	78,610,000	38,891,000
U.S. Treasury Securities [Member] | Recurring [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	78,610,000	38,891,000
U.S. Treasury Securities [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	78,610,000	38,891,000
U.S. Treasury Securities [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
U.S. Treasury Securities [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
Securities of U.S. Government Agencies and Corporations [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	100,658,000	106,558,000
Securities of U.S. Government Agencies and Corporations [Member] | Recurring [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	100,658,000	106,558,000
Securities of U.S. Government Agencies and Corporations [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
Securities of U.S. Government Agencies and Corporations [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	100,658,000	106,558,000
Securities of U.S. Government Agencies and Corporations [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
Obligations of States and Political Subdivisions [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	39,696,000	32,882,000
Obligations of States and Political Subdivisions [Member] | Recurring [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	39,696,000	32,882,000
Obligations of States and Political Subdivisions [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
Obligations of States and Political Subdivisions [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	39,696,000	32,882,000
Obligations of States and Political Subdivisions [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
Collateralized Mortgage Obligations [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	139,803,000	73,460,000
Collateralized Mortgage Obligations [Member] | Recurring [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	139,803,000	73,460,000
Collateralized Mortgage Obligations [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
Collateralized Mortgage Obligations [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	139,803,000	73,460,000
Collateralized Mortgage Obligations [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
Mortgage-backed Securities [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	258,343,000	183,289,000
Mortgage-backed Securities [Member] | Recurring [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	258,343,000	183,289,000
Mortgage-backed Securities [Member] | Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	0	0
Mortgage-backed Securities [Member] | Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	258,343,000	183,289,000
Mortgage-backed Securities [Member] | Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets Recorded at Fair Value on a Recurring Basis [Abstract]
Total investments at fair value	$ 0	$ 0