ALLOWANCE FOR LOAN LOSSES AND CREDIT QUALITY - Additional Information (Details)		12 Months Ended
	Jan. 20, 2021 USD ($) borrower	Dec. 31, 2020 USD ($) borrower	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Troubled Debt Restructuring
Loans Modified In Troubled Debt Restructured Loans		$ 5,500,000	$ 2,500,000
Valuation allowance		61,408,000	50,652,000	$ 48,453,000	$ 47,121,000
Financing Receivable, Troubled Debt Restructuring, Subsequent Default			601,000
Loan amount of credit quality analysis		250,000
Financing receivable, loan portfolio, deferrals, COVID-19	$ 102,200,000	$ 100,700,000
Financing receivable, loan portfolio, deferrals, COVID-19, borrowers | borrower	50	49
Financing receivable, loan portfolio, deferrals, COVID-19, percentage of loan portfolio (as a percent)	2.30%	2.20%
Loans		$ 4,649,156,000	4,065,828,000
Loans under second deferral action	$ 20,800,000
Loans under fourth deferral action	26,600,000
Borrowers percentage		90
Pass
Troubled Debt Restructuring
Loans		$ 3,997,245,000	$ 3,490,863,000
All Modifications [Member]
Troubled Debt Restructuring
Number of Loans		4,000	1	12
Construction and Land Development Loans [Member]
Troubled Debt Restructuring
Financing Receivable, Modifications, Recorded Investment		$ 2,200,000	$ 2,400,000	$ 1,400,000
Commercial and Industrial Loans [Member]
Troubled Debt Restructuring
Valuation allowance		28,333,000	25,789,000	22,518,000	21,097,000
Financing Receivable, Modifications, Recorded Investment				1,300,000
Loans		1,784,926,000	1,426,826,000
Commercial and Industrial Loans [Member] | Non-working Capital Loans [Member]
Troubled Debt Restructuring
Loans		1,158,827,000	716,843,000
Commercial and Industrial Loans [Member] | Non-working Capital Loans [Member] | Pass
Troubled Debt Restructuring
Loans		1,111,989,000	673,370,000
Commercial Real Estate and Multi-family Residential Loans
Troubled Debt Restructuring
Valuation allowance		22,907,000	15,796,000	15,393,000	14,714,000
Financing Receivable, Modifications, Recorded Investment			1,900,000
Loans		1,892,572,000	1,670,840,000
Agri-business and Agricultural Loans [Member]
Troubled Debt Restructuring
Valuation allowance		3,043,000	3,869,000	4,305,000	4,920,000
Loans		429,662,000	379,631,000
Consumer 1-4 Family Mortgage Loans [Member]
Troubled Debt Restructuring
Valuation allowance		2,619,000	2,086,000	2,292,000	$ 2,768,000
Increase (decrease) in allowance for loan loss		45,000	484,000	189,000
Financing Receivable, Modifications, Recorded Investment				$ 593,000
Loans		344,699,000	$ 377,999,000
Commercial loan
Troubled Debt Restructuring
Financing receivable, loan portfolio, deferrals, COVID-19	$ 99,700,000	$ 98,200,000
Financing receivable, loan portfolio, deferrals, COVID-19, borrowers | borrower	24	22
Financing receivable, loan portfolio, deferrals, COVID-19, percentage of loan portfolio (as a percent)	2.40%	2.30%
Loans under first deferral action		$ 11,900,000
Loans under second deferral action		22,800,000
Loans under third deferral action	$ 40,200,000	41,900,000
Loans under fourth deferral action		24,100,000
Consumer loan open-ended revolving lines
Troubled Debt Restructuring
Financing receivable, loan portfolio, deferrals, COVID-19	$ 2,500,000	$ 2,500,000
Financing receivable, loan portfolio, deferrals, COVID-19, borrowers | borrower	26	27
Financing receivable, loan portfolio, deferrals, COVID-19, percentage of loan portfolio (as a percent)	0.70%	0.70%
PPP | Pass
Troubled Debt Restructuring
Loans		$ 412,000,000.0