CONDENSED FINANCIAL INFORMATION - PARENT COMPANY ONLY (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets [Abstract]
Cash	$ 16,374,000				$ 17,727,000				$ 16,374,000	$ 17,727,000
Investments	295,189,000				240,706,000				295,189,000	240,706,000
OtherAssets	19,404,000				16,359,000				19,404,000	16,359,000
TOTAL ASSETS	1,891,674,000				1,466,339,000				1,891,674,000	1,466,339,000
Liabilities [Abstract]
OtherLiabilities	18,702,000				14,242,000				18,702,000	14,242,000
Borrowed funds	88,838,000				85,117,000				88,838,000	85,117,000
TOTAL LIABILITIES	1,697,415,000				1,311,565,000				1,697,415,000	1,311,565,000
Stockholders' equity	194,259,000				154,774,000				194,259,000	154,774,000	$ 139,229,000	$ 129,011,000
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	1,891,674,000				1,466,339,000				1,891,674,000	1,466,339,000
Dividends from [Abstract]
TOTAL INTEREST AND DIVIDEND INCOME	18,411,000	$ 18,386,000	$ 18,160,000	$ 15,339,000	15,587,000	$ 15,874,000	$ 15,502,000	$ 15,017,000	70,296,000	61,980,000	56,758,000
Realized securities gains (losses)									(41,000)	120,000	0
Expenses									6,481,000	5,682,000	5,294,000
NET INCOME	7,227,000	8,007,000	5,338,000	4,531,000	5,043,000	5,196,000	4,846,000	4,405,000	25,103,000	19,490,000	18,034,000
Comprehensive income									28,319,000	22,782,000	17,510,000
Cash flows from operating activities [Abstract]
Net income	7,227,000	$ 8,007,000	$ 5,338,000	4,531,000	5,043,000	$ 5,196,000	$ 4,846,000	4,405,000	25,103,000	19,490,000	18,034,000
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Investment securities (gains) losses, net									41,000	(120,000)	0
Other, net									1,580,000	(182,000)	787,000
Net cash (used in) provided by operating activities									11,822,000	21,767,000	21,486,000
Cash flows from investing activities [Abstract]
Purchases of equity securities									(143,987,000)	(68,963,000)	(67,899,000)
Proceeds from sale of equity securities									168,000	0	0
Net cash provided by (used in) investing activities									(110,734,000)	(32,323,000)	(72,351,000)
Cash flows from financing activities [Abstract]
Cash dividends paid									(6,539,000)	(6,315,000)	(6,116,000)
Purchase of treasury stock									(2,122,000)	(1,291,000)	(1,175,000)
Reissuance of treasury stock to employee stock purchase plan									126,000	0	0
Net cash provided by financing activities									149,099,000	12,279,000	49,145,000
Net increase (decrease) in cash and cash equivalents									50,187,000	1,723,000	(1,720,000)
Cash and Cash Equivalents at Beginning of Year				18,520,000				16,797,000	18,520,000	16,797,000	18,517,000
Cash and Cash Equivalents at End of Year	68,707,000				18,520,000				68,707,000	18,520,000	16,797,000
Parent Company [Member]
Assets [Abstract]
Cash	5,301,000				7,166,000				5,301,000	7,166,000
Investments	1,866,000				617,000				1,866,000	617,000
Investment in subsidiary	194,312,000				154,501,000				194,312,000	154,501,000
OtherAssets	846,000				744,000				846,000	744,000
TOTAL ASSETS	202,325,000				163,028,000				202,325,000	163,028,000
Liabilities [Abstract]
OtherLiabilities	566,000				754,000				566,000	754,000
Borrowed funds	7,500,000				7,500,000				7,500,000	7,500,000
TOTAL LIABILITIES	8,066,000				8,254,000				8,066,000	8,254,000
Stockholders' equity	194,259,000				154,774,000				194,259,000	154,774,000
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	202,325,000				163,028,000				202,325,000	163,028,000
Dividends from [Abstract]
Subsidiary									16,171,000	9,565,000	8,248,000
Equity securities									45,000	17,000	7,000
TOTAL INTEREST AND DIVIDEND INCOME									16,216,000	9,582,000	8,255,000
Realized securities gains (losses)									(23,000)	101,000	0
Expenses									775,000	1,103,000	642,000
Income before equity in undistributed earnings of subsidiary									15,418,000	8,580,000	7,613,000
Equity in undistributed earnings of subsidiary									9,685,000	10,910,000	10,421,000
NET INCOME									25,103,000	19,490,000	18,034,000
Comprehensive income									28,319,000	22,782,000	17,510,000
Cash flows from operating activities [Abstract]
Net income									25,103,000	19,490,000	18,034,000
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Equity in undistributed earnings of subsidiary									(9,685,000)	(10,910,000)	(10,421,000)
Investment securities (gains) losses, net									23,000	(101,000)	0
Other, net									14,000	717,000	(251,000)
Net cash (used in) provided by operating activities									15,455,000	9,196,000	7,362,000
Cash flows from investing activities [Abstract]
Purchases of equity securities									(1,339,000)	0	(425,000)
Proceeds from sale of equity securities									168,000	0	0
Acquisition of Midcoast									(7,614,000)
Net cash provided by (used in) investing activities									(8,785,000)	0	(425,000)
Cash flows from financing activities [Abstract]
Cash dividends paid									(6,539,000)	(6,315,000)	(6,116,000)
Purchase of treasury stock									(2,122,000)	(1,291,000)	(1,483,000)
Reissuance of treasury stock to employee stock purchase plan									126,000	0	0
Net cash provided by financing activities									(8,535,000)	(7,606,000)	(7,599,000)
Net increase (decrease) in cash and cash equivalents									(1,865,000)	1,590,000	(662,000)
Cash and Cash Equivalents at Beginning of Year				$ 7,166,000				$ 5,576,000	7,166,000	5,576,000	6,238,000
Cash and Cash Equivalents at End of Year	$ 5,301,000				$ 7,166,000				$ 5,301,000	$ 7,166,000	$ 5,576,000