INCOME TAXES (Details 1) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Computed statutory federal income tax provision									$ 47,091	$ 39,226	$ 32,262
State taxes, net of federal tax benefit									6,817	5,643	4,500
Revaluation of net deferred tax assets									1,895	0	0
Merger and other related costs (non-deductible)									213	210	185
Change in valuation allowance									31	28	41
New Markets Tax Credits									(3,960)	(6,360)	(6,514)
Increase in cash surrender value of life insurance									(1,445)	(1,431)	(1,292)
Stock-based compensation									(1,258)	0	0
Low Income Housing Project Investments									(1,253)	(1,641)	(1,182)
Nontaxable interest, net									(987)	(996)	(973)
Other, net									197	748	191
Total expense	$ 14,915	$ 12,681	$ 10,731	$ 9,014	$ 7,698	$ 9,793	$ 9,508	$ 8,428	$ 47,341	$ 35,427	$ 27,218
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Computed statutory federal income tax provision									35.00%	35.00%	35.00%
State taxes, net of federal tax benefit									5.07%	5.03%	4.88%
Revaluation of net deferred tax assets									1.41%	0.00%	0.00%
Merger and other related costs (non-deductible)									0.16%	0.19%	0.20%
Change in valuation allowance									0.02%	0.02%	0.04%
New Markets Tax Credits									(2.94%)	(5.67%)	(7.07%)
Increase in cash surrender value of life insurance									(1.07%)	(1.28%)	(1.40%)
Stock-based compensation									(0.94%)	(0.00%)	(0.00%)
Low Income Housing Project Investments									(0.93%)	(1.46%)	(1.28%)
Nontaxable interest, net									(0.73%)	(0.89%)	(1.06%)
Other, net									0.15%	0.67%	0.22%
Total expense									35.20%	31.61%	29.53%