ALLOWANCE FOR LOAN LOSSES AND CREDIT QUALITY - Additional Information (Details)		3 Months Ended	9 Months Ended
	Oct. 21, 2020 USD ($) borrower	Sep. 30, 2020 USD ($) borrower loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Troubled Debt Restructuring
Loans Modified In Troubled Debt Restructured Loans		$ 2,400,000	$ 2,400,000
Valuation allowance		60,747,000	60,747,000	$ 50,628,000	$ 59,019,000	$ 50,652,000	$ 50,564,000		$ 48,453,000
Loan amount of credit quality analysis			250,000
Financing receivable, loan portfolio, deferrals, COVID-19	$ 110,500,000	$ 158,400,000
Financing receivable, loan portfolio, deferrals, COVID-19, borrowers | borrower	63	102
Financing receivable, loan portfolio, deferrals, COVID-19, percentage of loan portfolio (as a percent)	2.40%	3.40%
Charge-offs recorded for new troubled debt restructurings			666,000
Loans		$ 4,589,924,000	$ 4,589,924,000			4,065,828,000
Loans modified as troubled debt restructurings | loan		0	0
Borrowers percentage		84
Pass
Troubled Debt Restructuring
Loans		$ 3,995,113,000	$ 3,995,113,000			3,490,863,000
All Modifications [Member]
Troubled Debt Restructuring
Loans Modified In Troubled Debt Restructured Loans		4,700,000	$ 4,700,000			2,500,000
Number of Loans | loan			4	1
Commercial and Industrial Loans [Member]
Troubled Debt Restructuring
Valuation allowance		28,363,000	$ 28,363,000	$ 24,977,000	26,744,000	25,789,000	25,024,000		22,518,000
Loans		1,837,747,000	1,837,747,000			1,426,826,000
Commercial and Industrial Loans [Member] | Non-working Capital Loans [Member]
Troubled Debt Restructuring
Loans		1,245,107,000	1,245,107,000			716,843,000
Commercial and Industrial Loans [Member] | Non-working Capital Loans [Member] | Pass
Troubled Debt Restructuring
Loans		1,195,861,000	1,195,861,000			673,370,000
Commercial Real Estate and Multi-family Residential Loans [Member]
Troubled Debt Restructuring
Valuation allowance		21,415,000	21,415,000	16,010,000	21,063,000	15,796,000	15,492,000		15,393,000
Loans		1,857,820,000	1,857,820,000			1,670,840,000
Agri-business and Agricultural Loans [Member]
Troubled Debt Restructuring
Valuation allowance		3,097,000	3,097,000	3,904,000	3,408,000	3,869,000	3,906,000		4,305,000
Loans		338,164,000	338,164,000			379,631,000
Consumer 1-4 Family Mortgage Loans [Member]
Troubled Debt Restructuring
Valuation allowance		3,318,000	3,318,000	$ 2,120,000	$ 3,434,000	2,086,000	$ 2,153,000		$ 2,292,000
Loans		353,724,000	353,724,000			$ 377,999,000
Commercial Real Estate Building
Troubled Debt Restructuring
Financing Receivable, Modifications, Recorded Investment								$ 533,000
Commercial and Industrial Nonworking Capital
Troubled Debt Restructuring
Financing Receivable, Modifications, Recorded Investment								$ 70,000
Commercial Real Estates
Troubled Debt Restructuring
Valuation allowance		63,000	63,000
Commercial Loan
Troubled Debt Restructuring
Financing receivable, loan portfolio, deferrals, COVID-19	$ 107,500,000	$ 155,200,000
Financing receivable, loan portfolio, deferrals, COVID-19, borrowers | borrower	37	71
Financing receivable, loan portfolio, deferrals, COVID-19, percentage of loan portfolio (as a percent)	2.50%	3.70%
Loans under first deferral action	$ 8,100,000	$ 15,300,000
Loans under second deferral action	69,800,000	116,200,000
Loans under third deferral action	29,700,000	23,700,000
Consumer Loan
Troubled Debt Restructuring
Financing receivable, loan portfolio, deferrals, COVID-19	$ 3,000,000.0	$ 3,300,000
Financing receivable, loan portfolio, deferrals, COVID-19, borrowers | borrower	26	31
Financing receivable, loan portfolio, deferrals, COVID-19, percentage of loan portfolio (as a percent)	0.80%	0.90%
PPP | Pass
Troubled Debt Restructuring
Loans		$ 557,900,000	$ 557,900,000