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INCOME TAXES (Details 1) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
INCOME TAXES (Details 1) - USD ($) $ in Thousands	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 Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Computed statutory federal income tax provision									$ 45,803	$ 32,744	$ 47,091
State taxes, net of federal tax benefit									12,262	9,633	6,817
Merger and other related costs (non-deductible)									582	130	213
Change in valuation allowance									17	49	31
Effective Income Tax Rate Reconciliation, Revaluation of Net Deferred Tax Assets									0	0	1,895
New Markets Tax Credits									(2,675)	(3,960)	(3,960)
Increase in cash surrender value of life insurance									(1,144)	(1,160)	(1,445)
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount									(1,696)	(1,030)	(1,253)
Stock-based compensation									(824)	(885)	(1,258)
Nontaxable interest, net									(757)	(566)	(987)
Other, net									1,365	(651)	197
Total expense	$ 14,368	$ 17,036	$ 10,007	$ 11,522	$ 8,258	$ 9,969	$ 9,249	$ 6,828	$ 52,933	$ 34,304	$ 47,341
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Computed statutory federal income tax provision									21.00%	21.00%	35.00%
State taxes, net of federal tax benefit									5.63%	6.18%	5.07%
Merger and other related costs (non-deductible)									0.27%	0.08%	0.16%
Change in valuation allowance									0.01%	0.03%	0.02%
Effective Income Tax Rate Reconciliation, Revaluation of Net Deferred Tax Asset, Percent									0.00%	0.00%	1.41%
New Markets Tax Credits									(1.23%)	(2.54%)	(2.94%)
Increase in cash surrender value of life insurance									(0.52%)	(0.74%)	(1.07%)
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Percent									(0.78%)	(0.66%)	(0.93%)
Stock-based compensation									(0.38%)	(0.57%)	(0.94%)
Nontaxable interest, net									(0.35%)	(0.36%)	(0.73%)
Other, net									0.63%	(0.42%)	0.15%
Total expense									24.28%	22.00%	35.20%