LOANS (Carrying amount of loans acquired) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	$ 1,609,852	$ 1,633,331
Commercial | Commercial
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	266,936	247,494
Commercial | Commercial real estate
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	1,089,596	1,098,329
Agricultural and agricultural real estate
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	9,827	27,115
Residential real estate
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	157,575	184,620
Consumer
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	85,918	75,773
Impaired Purchased Loans
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	10,004	4,190
Impaired Purchased Loans | Commercial | Commercial
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	6,744	3,801
Impaired Purchased Loans | Commercial | Commercial real estate
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	3,260	158
Impaired Purchased Loans | Agricultural and agricultural real estate
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	0	0
Impaired Purchased Loans | Residential real estate
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	0	231
Impaired Purchased Loans | Consumer
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	0	0
Non Impaired Purchased Loans
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	1,599,848	1,629,141
Non Impaired Purchased Loans | Commercial | Commercial
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	260,192	243,693
Non Impaired Purchased Loans | Commercial | Commercial real estate
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	1,086,336	1,098,171
Non Impaired Purchased Loans | Agricultural and agricultural real estate
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	9,827	27,115
Non Impaired Purchased Loans | Residential real estate
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	157,575	184,389
Non Impaired Purchased Loans | Consumer
Loans covered by loss share agreement (carrying amount) [Line Items]
Purchased loans	$ 85,918	$ 75,773