INCOME TAXES - Computation of Differences Between Financial Statement Tax Expense And Amounts (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
INCOME TAXES
Income taxes at statutory federal rate of 21% (2019 and 2018) and 35% (2017)									$ 22,551,000	$ 20,778,000	$ 31,372,000
Increase (decrease) in taxes resulting from:
Tax exempt income									(1,682,000)	(1,434,000)	(2,015,000)
Nondeductible expense									194,000	165,000	193,000
State income tax, net of federal tax effect									1,040,000	1,077,000	846,000
Captive insurance premium income									(310,000)	(292,000)	(378,000)
Tax credits									(548,000)	(412,000)	(326,000)
Bank owned life insurance									(573,000)	(303,000)	(619,000)
Long - term incentive plan									(421,000)	(641,000)	(854,000)
Revaluation deferred tax asset at 21% rate									0	(408,000)	4,137,000
Other									87,000	3,000	(52,000)
Total income tax expense	$ 5,431,000	$ 5,119,000	$ 5,409,000	$ 4,379,000	$ 5,480,000	$ 4,679,000	$ 5,110,000	$ 3,264,000	$ 20,338,000	$ 18,533,000	$ 32,304,000