LOANS (Troubled debt restructuring) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	2	0	4	4
Pre- Modification Recorded Investment	$ 9,454	$ 0	$ 9,546	$ 276
Post- Modification Recorded Investment	$ 9,454	$ 0	$ 9,552	$ 288
With Payment Defaults
Number of Loans | loan	0	0	1	3
Recorded Investment	$ 0	$ 0	$ 236	$ 253
Total Past Due	16,817		16,817			$ 31,928
Current	9,003,789		9,003,789			8,259,441
Nonaccrual	79,040		79,040			76,548
Loans receivable	9,099,646		9,099,646			8,367,917
Allowance for credit loss	103,377	66,222	103,377	66,222	$ 119,937	70,395	$ 63,850	$ 61,963
Charge-offs	(21,753)	(4,842)	(31,618)	(11,572)
Recoveries	452	2,013	2,916	4,077
Provision for Loan and Lease Losses			49,994	11,754
Provision	4,741	$ 5,201	49,613	$ 11,754
Cumulative Effect, Period of Adoption, Adjustment
With Payment Defaults
Allowance for credit loss						12,071
30-59 Days Past Due
With Payment Defaults
Total Past Due	9,533		9,533			25,322
60-89 Days Past Due
With Payment Defaults
Total Past Due	5,603		5,603			2,501
90 Days or More Past Due
With Payment Defaults
Total Past Due	$ 1,681		$ 1,681			4,105
Commercial and industrial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	1	0	1	0
Pre- Modification Recorded Investment	$ 20	$ 0	$ 20	$ 0
Post- Modification Recorded Investment	$ 20	$ 0	$ 20	$ 0
With Payment Defaults
Number of Loans | loan	0	0	0	0
Recorded Investment	$ 0	$ 0	$ 0	$ 0
Total Past Due	5,924		5,924			9,924
Current	2,276,336		2,276,336			2,491,110
Nonaccrual	21,386		21,386			29,775
Loans receivable	2,303,646		2,303,646			2,530,809
Allowance for credit loss	34,598	28,424	34,598	28,424	32,531	30,787	27,680	26,306
Charge-offs	(7,077)	(2,656)	(15,440)	(7,607)
Recoveries	369	1,526	1,153	2,110
Provision	8,775	$ 1,874	14,951	$ 7,615
Commercial and industrial | Commercial and industrial | Cumulative Effect, Period of Adoption, Adjustment
With Payment Defaults
Allowance for credit loss						3,147
Commercial and industrial | Commercial and industrial | 30-59 Days Past Due
With Payment Defaults
Total Past Due	3,200		3,200			5,121
Commercial and industrial | Commercial and industrial | 60-89 Days Past Due
With Payment Defaults
Total Past Due	2,293		2,293			904
Commercial and industrial | Commercial and industrial | 90 Days or More Past Due
With Payment Defaults
Total Past Due	$ 431		$ 431			3,899
Commercial and industrial | Paycheck Protection Program ("PPP")
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	0	0	0	0
Pre- Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
Post- Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
With Payment Defaults
Number of Loans | loan	0	0	0	0
Recorded Investment	$ 0	$ 0	$ 0	$ 0
Total Past Due	0		0
Current	1,128,035		1,128,035
Nonaccrual	0		0
Loans receivable	1,128,035		1,128,035			0
Allowance for credit loss	0		0		0	0
Charge-offs	0		0
Recoveries	0		0
Provision	0		0
Commercial and industrial | Paycheck Protection Program ("PPP") | Cumulative Effect, Period of Adoption, Adjustment
With Payment Defaults
Allowance for credit loss						0
Commercial and industrial | Paycheck Protection Program ("PPP") | 30-59 Days Past Due
With Payment Defaults
Total Past Due	0		0
Commercial and industrial | Paycheck Protection Program ("PPP") | 60-89 Days Past Due
With Payment Defaults
Total Past Due	0		0
Commercial and industrial | Paycheck Protection Program ("PPP") | 90 Days or More Past Due
With Payment Defaults
Total Past Due	$ 0		$ 0
Commercial and industrial | Owner occupied commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	0	0	0	0
Pre- Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
Post- Modification Recorded Investment	0	0	$ 0	$ 0
With Payment Defaults
Number of Loans | loan			0	0
Recorded Investment			$ 0	$ 0
Total Past Due	1,948		1,948			4,177
Current	1,479,890		1,479,890			1,461,589
Nonaccrual	13,064		13,064			6,938
Loans receivable	1,494,902		1,494,902			1,472,704
Allowance for credit loss	11,229	7,250	11,229	7,250	23,402	8,214	6,182	6,525
Charge-offs	(13,328)	(43)	(13,541)	(79)
Recoveries	0	3	192	96
Provision	1,155	$ 1,108	16,771	$ 708
Commercial and industrial | Owner occupied commercial real estate | Cumulative Effect, Period of Adoption, Adjustment
With Payment Defaults
Allowance for credit loss						(407)
Commercial and industrial | Owner occupied commercial real estate | 30-59 Days Past Due
With Payment Defaults
Total Past Due	1,052		1,052			3,487
Commercial and industrial | Owner occupied commercial real estate | 60-89 Days Past Due
With Payment Defaults
Total Past Due	896		896			690
Commercial and industrial | Owner occupied commercial real estate | 90 Days or More Past Due
With Payment Defaults
Total Past Due	$ 0		$ 0			0
Commercial and industrial | Non-owner occupied commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	1	0	1	0
Pre- Modification Recorded Investment	$ 9,434	$ 0	$ 9,434	$ 0
Post- Modification Recorded Investment	9,434	0	$ 9,434	$ 0
With Payment Defaults
Number of Loans | loan			0	0
Recorded Investment			$ 0	$ 0
Total Past Due	2,548		2,548			695
Current	1,653,491		1,653,491			1,493,619
Nonaccrual	3,644		3,644			1,563
Loans receivable	1,659,683		1,659,683			1,495,877
Allowance for credit loss	12,127	7,747	12,127	7,747	10,162	7,802	7,482	7,430
Charge-offs	(26)	(21)	(45)	(21)
Recoveries	10	100	18	200
Provision	1,981	$ 186	7,186	$ 138
Commercial and industrial | Non-owner occupied commercial real estate | Cumulative Effect, Period of Adoption, Adjustment
With Payment Defaults
Allowance for credit loss						(2,834)
Commercial and industrial | Non-owner occupied commercial real estate | 30-59 Days Past Due
With Payment Defaults
Total Past Due	863		863			614
Commercial and industrial | Non-owner occupied commercial real estate | 60-89 Days Past Due
With Payment Defaults
Total Past Due	1,685		1,685			81
Commercial and industrial | Non-owner occupied commercial real estate | 90 Days or More Past Due
With Payment Defaults
Total Past Due	$ 0		$ 0			0
Commercial and industrial | Real estate construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	0	0	0	0
Pre- Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
Post- Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
With Payment Defaults
Number of Loans | loan	0	0	0	0
Recorded Investment	$ 0	$ 0	$ 0	$ 0
Total Past Due	907		907			5,761
Current	915,205		915,205			1,020,153
Nonaccrual	1,653		1,653			1,167
Loans receivable	917,765		917,765			1,027,081
Allowance for credit loss	20,787	10,688	20,787	10,688	28,667	11,599	10,010	9,679
Charge-offs	0	0	(105)	(155)
Recoveries	2	38	217	166
Provision	(7,882)	$ 640	5,663	$ 998
Commercial and industrial | Real estate construction | Cumulative Effect, Period of Adoption, Adjustment
With Payment Defaults
Allowance for credit loss						3,413
Commercial and industrial | Real estate construction | 30-59 Days Past Due
With Payment Defaults
Total Past Due	310		310			5,689
Commercial and industrial | Real estate construction | 60-89 Days Past Due
With Payment Defaults
Total Past Due	597		597			72
Commercial and industrial | Real estate construction | 90 Days or More Past Due
With Payment Defaults
Total Past Due	$ 0		$ 0			0
Agricultural and agricultural real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	0	0	0	0
Pre- Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
Post- Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
With Payment Defaults
Number of Loans | loan	0	0	0	0
Recorded Investment	$ 0	$ 0	$ 0	$ 0
Total Past Due	1,308		1,308			3,839
Current	488,175		488,175			541,455
Nonaccrual	18,575		18,575			20,543
Loans receivable	508,058		508,058			565,837
Allowance for credit loss	5,341	5,370	5,341	5,370	5,701	5,673	5,986	4,914
Charge-offs	(936)	(1,673)	(1,190)	(2,100)
Recoveries	0	199	826	528
Provision	576	$ 858	412	$ 2,028
Agricultural and agricultural real estate | Cumulative Effect, Period of Adoption, Adjustment
With Payment Defaults
Allowance for credit loss						(380)
Agricultural and agricultural real estate | 30-59 Days Past Due
With Payment Defaults
Total Past Due	1,308		1,308			3,734
Agricultural and agricultural real estate | 60-89 Days Past Due
With Payment Defaults
Total Past Due	0		0			79
Agricultural and agricultural real estate | 90 Days or More Past Due
With Payment Defaults
Total Past Due	$ 0		$ 0			26
Residential real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	0	0	2	4
Pre- Modification Recorded Investment	$ 0	$ 0	$ 92	$ 276
Post- Modification Recorded Investment	$ 0	$ 0	$ 98	$ 288
With Payment Defaults
Number of Loans | loan	0	0	1	3
Recorded Investment	$ 0	$ 0	$ 236	$ 253
Total Past Due	3,156		3,156			4,370
Current	682,217		682,217			814,840
Nonaccrual	16,526		16,526			13,067
Loans receivable	701,899		701,899			832,277
Allowance for credit loss	9,671	1,805	9,671	1,805	9,304	1,504	1,592	1,813
Charge-offs	(54)	(3)	(368)	(344)
Recoveries	2	52	97	138
Provision	419	$ 164	3,621	$ 198
Residential real estate | Cumulative Effect, Period of Adoption, Adjustment
With Payment Defaults
Allowance for credit loss						4,817
Residential real estate | 30-59 Days Past Due
With Payment Defaults
Total Past Due	1,820		1,820			4,166
Residential real estate | 60-89 Days Past Due
With Payment Defaults
Total Past Due	86		86			24
Residential real estate | 90 Days or More Past Due
With Payment Defaults
Total Past Due	$ 1,250		$ 1,250			180
Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | loan	0	0	0	0
Pre- Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
Post- Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
With Payment Defaults
Number of Loans | loan	0	0	0	0
Recorded Investment	$ 0	$ 0	$ 0	$ 0
Total Past Due	1,026		1,026			3,162
Current	380,440		380,440			436,675
Nonaccrual	4,192		4,192			3,495
Loans receivable	385,658		385,658			443,332
Allowance for credit loss	9,624	4,938	9,624	4,938	$ 10,170	4,816	$ 4,918	$ 5,296
Charge-offs	(332)	(446)	(929)	(1,266)
Recoveries	69	95	413	839
Provision	(283)	$ 371	1,009	$ 69
Consumer | Cumulative Effect, Period of Adoption, Adjustment
With Payment Defaults
Allowance for credit loss						4,315
Consumer | 30-59 Days Past Due
With Payment Defaults
Total Past Due	980		980			2,511
Consumer | 60-89 Days Past Due
With Payment Defaults
Total Past Due	46		46			651
Consumer | 90 Days or More Past Due
With Payment Defaults
Total Past Due	$ 0		$ 0			$ 0