LOANS - Total Loans Outstanding (Details) - USD ($) $ in Thousands		9 Months Ended		12 Months Ended
		Sep. 30, 2021		Dec. 31, 2020		Jun. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 4,244,354
Less: Allowance for credit losses		(73,048)	[1]	$ (61,408)		$ (71,713)
Net deferred loan fees		(4,901)
Loans, net	[1]	$ 4,166,405
Percentage of loans receivable		100.00%		100.00%
Loans and leases receivable, gross				$ 4,657,183
Less: Allowance for credit losses				(61,408)	[1]		$ (60,747)	$ (59,019)	$ (50,652)
Net deferred loan fees				(8,027)
Loans, net	[1]			$ 4,587,748
Total commercial loans | Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 3,804,013
Percentage of loans receivable		89.60%		90.40%
Loans and leases receivable, gross				$ 4,210,049
Total consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 440,341
Percentage of loans receivable		10.40%		9.60%
Loans and leases receivable, gross				$ 447,134
Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 92,169
Percentage of loans receivable		2.20%		2.20%
Loans and leases receivable, gross				$ 103,616
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 1,441,784
Percentage of loans receivable		34.00%		38.50%
Loans and leases receivable, gross				$ 1,791,378
Less: Allowance for credit losses				(28,333)			(28,363)	(26,744)	(25,789)
Commercial and industrial loans | Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: Allowance for credit losses		$ (36,676)		$ (28,333)		(33,130)
Commercial and industrial loans | Working capital lines of credit loans | Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 659,166
Percentage of loans receivable		15.50%		13.50%
Loans and leases receivable, gross				$ 626,023
Commercial and industrial loans | Non-working capital loans | Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 782,618
Percentage of loans receivable		18.50%		25.00%
Loans and leases receivable, gross				$ 1,165,355
Commercial real estate and multi-family residential loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 1,954,554
Percentage of loans receivable		46.00%		40.70%
Loans and leases receivable, gross				$ 1,895,014
Commercial real estate and multi-family residential loans | Construction and land development loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 378,716
Percentage of loans receivable		8.90%		7.80%
Loans and leases receivable, gross				$ 362,653
Commercial real estate and multi-family residential loans | Owner occupied loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 740,836
Percentage of loans receivable		17.40%		13.90%
Loans and leases receivable, gross				$ 648,019
Commercial real estate and multi-family residential loans | Nonowner occupied loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 582,019
Percentage of loans receivable		13.70%		12.50%
Loans and leases receivable, gross				$ 579,625
Commercial real estate and multi-family residential loans | Multifamily loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 252,983
Percentage of loans receivable		6.00%		6.50%
Loans and leases receivable, gross				$ 304,717
Agri-business and agricultural loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 324,080
Percentage of loans receivable		7.60%		9.20%
Loans and leases receivable, gross				$ 429,644
Less: Allowance for credit losses				(3,043)			$ (3,097)	$ (3,408)	$ (3,869)
Agri-business and agricultural loans | Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: Allowance for credit losses		$ (3,686)		$ (3,043)		$ (3,930)
Agri-business and agricultural loans | Loans secured by farmland | Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 152,099
Percentage of loans receivable		3.50%		4.20%
Loans and leases receivable, gross				$ 195,410
Agri-business and agricultural loans | Loans for agricultural production | Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 171,981
Percentage of loans receivable		4.10%		5.00%
Loans and leases receivable, gross				$ 234,234
Other commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 83,595
Percentage of loans receivable		2.00%		2.00%
Loans and leases receivable, gross				$ 94,013
Consumer 1-4 family mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 348,172
Percentage of loans receivable		8.20%		7.40%
Loans and leases receivable, gross				$ 343,518
Consumer 1-4 family mortgage loans | Closed end first mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 173,689
Percentage of loans receivable		4.10%		3.60%
Loans and leases receivable, gross				$ 167,847
Consumer 1-4 family mortgage loans | Open end and junior lien loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 161,941
Percentage of loans receivable		3.80%		3.50%
Loans and leases receivable, gross				$ 163,664
Consumer 1-4 family mortgage loans | Residential construction and land development loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable before allowance for credit loss		$ 12,542
Percentage of loans receivable		0.30%		0.30%
Loans and leases receivable, gross				$ 12,007

[1] Beginning January 1, 2021 calculation is based on the current expected credit loss methodology. Prior to January 1, 2021 calculation was based on the incurred loss methodology.