LOANS - Summary of Total Loans (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) item	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 2,708,691	$ 2,641,092
Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,056,846	1,835,230
Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	651,845	805,862
Acquired Loans | Financial Asset Acquired with Credit Deterioration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	14,200
Total note balances	18,100
Acquired Loans | Financial Asset Acquired and No Credit Deterioration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	637,600
Total commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,568,145	1,353,952
Total commercial loans | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,293,519	1,024,008
Total commercial loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	274,626	329,944
Total commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,045,635	930,661
Total commercial real estate | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	852,398	697,438
Total commercial real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	193,237	233,223
Total commercial real estate | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	89,118	34,290
Total commercial real estate | Construction and land development | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	86,927	31,387
Total commercial real estate | Construction and land development | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,191	2,903
Total commercial real estate | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	956,517	896,371
Total commercial real estate | Other commercial real estate | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	765,471	666,051
Total commercial real estate | Other commercial real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	191,046	230,320
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	522,510	423,291
Commercial and industrial | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	441,121	326,570
Commercial and industrial | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	81,389	96,721
Commercial and industrial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	438,370	298,764
Commercial and industrial | Commercial | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	381,512	239,692
Commercial and industrial | Commercial | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	56,858	59,072
Commercial and industrial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,814	20,224
Commercial and industrial | Agricultural | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	17,658	20,018
Commercial and industrial | Agricultural | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	156	206
Commercial and industrial | Tax exempt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	66,326	104,303
Commercial and industrial | Tax exempt | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	41,951	66,860
Commercial and industrial | Tax exempt | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	24,375	37,443
Total residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 1,021,206	1,151,857
Total residential real estate | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of families | item	4
Total residential real estate | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of families | item	1
Total residential real estate | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 695,766	740,687
Total residential real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	325,440	411,170
Total residential real estate | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,021,206	1,151,857
Total residential real estate | Residential mortgages | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	695,766	740,687
Total residential real estate | Residential mortgages | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	325,440	411,170
Total consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	119,340	135,283
Total consumer | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	67,561	70,535
Total consumer | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	51,779	64,748
Total consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	108,874	122,401
Total consumer | Home equity | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	58,344	59,368
Total consumer | Home equity | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	50,530	63,033
Total consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	10,466	12,882
Total consumer | Other consumer | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,217	11,167
Total consumer | Other consumer | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 1,249	$ 1,715