INCOME TAXES - Computation of Differences Between Financial Statement Tax Expense And Amounts (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
INCOME TAXES
Income taxes at statutory federal rate of 21%									$ 21,814,000	$ 22,551,000	$ 20,778,000
Increase (decrease) in taxes resulting from:
Tax exempt income									(1,925,000)	(1,682,000)	(1,434,000)
Nondeductible expense									117,000	194,000	165,000
State income tax, net of federal tax effect									944,000	1,040,000	1,077,000
Captive insurance premium income									(227,000)	(310,000)	(292,000)
Tax credits									(540,000)	(548,000)	(412,000)
Bank owned life insurance									(595,000)	(573,000)	(303,000)
Long - term incentive plan									(58,000)	(421,000)	(641,000)
Revaluation deferred tax asset at 21% rate											(408,000)
Other									9,000	87,000	3,000
Total income tax expense	$ 6,071,000	$ 5,377,000	$ 4,448,000	$ 3,643,000	$ 5,431,000	$ 5,119,000	$ 5,409,000	$ 4,379,000	$ 19,539,000	$ 20,338,000	$ 18,533,000