LOANS (Loans by credit quality indicator) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	$ 901,120	$ 3,119,680
Year Two	2,838,862	1,842,640
Year Three	1,689,532	1,287,023
Year Four	1,126,940	842,221
Year Five	769,848	485,454
Year Six and Prior	1,610,726	1,254,784
Revolving	1,113,428	1,191,249
Total	10,050,456	10,023,051
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	865,239	2,847,203
Year Two	2,595,223	1,649,219
Year Three	1,487,367	1,131,756
Year Four	927,474	727,712
Year Five	662,498	408,380
Year Six and Prior	1,377,044	1,091,908
Revolving	983,115	1,084,202
Total	8,897,960	8,940,380
Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	14,091	129,037
Year Two	111,595	141,385
Year Three	162,256	80,970
Year Four	129,962	58,813
Year Five	60,126	44,512
Year Six and Prior	124,465	76,144
Revolving	102,806	74,056
Total	705,301	604,917
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	21,790	143,440
Year Two	132,044	52,036
Year Three	39,909	74,297
Year Four	69,504	55,696
Year Five	47,224	32,562
Year Six and Prior	109,217	86,732
Revolving	27,507	32,991
Total	447,195	477,754
Commercial and industrial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	87,097	622,451
Year Two	579,229	381,759
Year Three	339,138	197,442
Year Four	170,699	245,675
Year Five	233,491	118,180
Year Six and Prior	434,409	359,845
Revolving	577,197	609,447
Total	2,421,260	2,534,799
Commercial and industrial | Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	85,059	557,853
Year Two	523,968	340,809
Year Three	305,803	168,873
Year Four	142,927	215,696
Year Five	206,293	101,010
Year Six and Prior	386,530	337,834
Revolving	481,837	541,627
Total	2,132,417	2,263,702
Commercial and industrial | Commercial and industrial | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	1,213	41,574
Year Two	31,058	24,676
Year Three	23,144	19,672
Year Four	19,494	14,262
Year Five	15,308	8,072
Year Six and Prior	21,877	2,474
Revolving	78,657	49,432
Total	190,751	160,162
Commercial and industrial | Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	825	23,024
Year Two	24,203	16,274
Year Three	10,191	8,897
Year Four	8,278	15,717
Year Five	11,890	9,098
Year Six and Prior	26,002	19,537
Revolving	16,703	18,388
Total	98,092	110,935
Commercial and industrial | Paycheck Protection Program ("PPP")
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	415,501	957,785
Year Two	739,827	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Year Six and Prior	0	0
Revolving	0	0
Total	1,155,328	957,785
Commercial and industrial | Paycheck Protection Program ("PPP") | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	400,126	880,709
Year Two	671,099	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Year Six and Prior	0	0
Revolving	0	0
Total	1,071,225	880,709
Commercial and industrial | Paycheck Protection Program ("PPP") | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	9,625	22,533
Year Two	20,344	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Year Six and Prior	0	0
Revolving	0	0
Total	29,969	22,533
Commercial and industrial | Paycheck Protection Program ("PPP") | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	5,750	54,543
Year Two	48,384	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Year Six and Prior	0	0
Revolving	0	0
Total	54,134	54,543
Commercial and industrial | Owner occupied commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	100,573	431,921
Year Two	446,836	392,687
Year Three	417,813	334,894
Year Four	304,119	202,428
Year Five	185,570	124,531
Year Six and Prior	337,893	250,770
Revolving	44,755	39,175
Total	1,837,559	1,776,406
Commercial and industrial | Owner occupied commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	97,898	400,662
Year Two	415,729	369,401
Year Three	387,953	300,242
Year Four	271,720	167,470
Year Five	152,313	107,234
Year Six and Prior	289,744	213,780
Revolving	36,676	33,759
Total	1,652,033	1,592,548
Commercial and industrial | Owner occupied commercial real estate | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	768	15,345
Year Two	16,775	13,764
Year Three	22,063	22,488
Year Four	22,059	20,811
Year Five	20,427	8,717
Year Six and Prior	19,212	15,282
Revolving	7,131	4,311
Total	108,435	100,718
Commercial and industrial | Owner occupied commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	1,907	15,914
Year Two	14,332	9,522
Year Three	7,797	12,164
Year Four	10,340	14,147
Year Five	12,830	8,580
Year Six and Prior	28,937	21,708
Revolving	948	1,105
Total	77,091	83,140
Commercial and industrial | Non-owner occupied commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	96,996	388,447
Year Two	385,704	481,561
Year Three	484,335	353,464
Year Four	351,685	229,871
Year Five	217,284	138,171
Year Six and Prior	406,012	299,885
Revolving	25,167	30,082
Total	1,967,183	1,921,481
Commercial and industrial | Non-owner occupied commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	94,856	334,722
Year Two	334,303	411,301
Year Three	379,230	305,456
Year Four	297,195	194,101
Year Five	181,937	108,070
Year Six and Prior	307,473	233,153
Revolving	20,154	24,466
Total	1,615,148	1,611,269
Commercial and industrial | Non-owner occupied commercial real estate | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	22,826
Year Two	20,932	55,225
Year Three	91,095	24,718
Year Four	31,107	18,724
Year Five	20,494	20,954
Year Six and Prior	67,914	45,672
Revolving	5,013	5,114
Total	236,555	193,233
Commercial and industrial | Non-owner occupied commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	2,140	30,899
Year Two	30,469	15,035
Year Three	14,010	23,290
Year Four	23,383	17,046
Year Five	14,853	9,147
Year Six and Prior	30,625	21,060
Revolving	0	502
Total	115,480	116,979
Commercial and industrial | Real estate construction
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	66,801	313,926
Year Two	345,206	339,097
Year Three	240,537	161,610
Year Four	103,533	12,957
Year Five	11,047	7,048
Year Six and Prior	9,901	5,856
Revolving	19,002	22,726
Total	796,027	863,220
Commercial and industrial | Real estate construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	66,643	311,625
Year Two	342,374	309,678
Year Three	229,345	157,171
Year Four	54,006	12,625
Year Five	10,730	6,954
Year Six and Prior	9,485	5,110
Revolving	18,588	21,431
Total	731,171	824,594
Commercial and industrial | Real estate construction | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	2,105
Year Two	2,832	26,659
Year Three	11,164	2,403
Year Four	47,532	332
Year Five	317	55
Year Six and Prior	25	388
Revolving	414	1,295
Total	62,284	33,237
Commercial and industrial | Real estate construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	158	196
Year Two	0	2,760
Year Three	28	2,036
Year Four	1,995	0
Year Five	0	39
Year Six and Prior	391	358
Revolving	0	0
Total	2,572	5,389
Agricultural and agricultural real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	64,428	209,481
Year Two	180,587	114,190
Year Three	100,997	94,722
Year Four	78,358	48,458
Year Five	40,419	25,058
Year Six and Prior	68,202	50,805
Revolving	150,978	171,812
Total	683,969	714,526
Agricultural and agricultural real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	56,474	171,578
Year Two	149,863	90,944
Year Three	81,301	62,349
Year Four	49,483	39,252
Year Five	32,928	17,626
Year Six and Prior	49,165	37,696
Revolving	132,606	148,456
Total	551,820	567,901
Agricultural and agricultural real estate | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	1,268	20,500
Year Two	17,561	16,202
Year Three	12,753	8,854
Year Four	6,863	2,448
Year Five	1,636	3,515
Year Six and Prior	6,667	3,157
Revolving	10,136	12,282
Total	56,884	66,958
Agricultural and agricultural real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	6,686	17,403
Year Two	13,163	7,044
Year Three	6,943	23,519
Year Four	22,012	6,758
Year Five	5,855	3,917
Year Six and Prior	12,370	9,952
Revolving	8,236	11,074
Total	75,265	79,667
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	52,212	157,983
Year Two	128,210	104,389
Year Three	82,501	123,549
Year Four	100,024	86,958
Year Five	67,991	67,478
Year Six and Prior	328,622	265,518
Revolving	27,434	34,567
Total	786,994	840,442
Residential real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	46,700	153,017
Year Two	125,274	99,440
Year Three	80,624	118,854
Year Four	95,884	83,534
Year Five	64,961	63,477
Year Six and Prior	312,167	244,852
Revolving	26,634	33,467
Total	752,244	796,641
Residential real estate | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	1,188	3,986
Year Two	1,989	4,507
Year Three	1,676	2,188
Year Four	2,067	1,896
Year Five	1,620	3,117
Year Six and Prior	8,062	8,525
Revolving	0	0
Total	16,602	24,219
Residential real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	4,324	980
Year Two	947	442
Year Three	201	2,507
Year Four	2,073	1,528
Year Five	1,410	884
Year Six and Prior	8,393	12,141
Revolving	800	1,100
Total	18,148	19,582
Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	17,512	37,686
Year Two	33,263	28,957
Year Three	24,211	21,342
Year Four	18,522	15,874
Year Five	14,046	4,988
Year Six and Prior	25,687	22,105
Revolving	268,895	283,440
Total	402,136	414,392
Consumer | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	17,483	37,037
Year Two	32,613	27,646
Year Three	23,111	18,811
Year Four	16,259	15,034
Year Five	13,336	4,009
Year Six and Prior	22,480	19,483
Revolving	266,620	280,996
Total	391,902	403,016
Consumer | Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	29	168
Year Two	104	352
Year Three	361	647
Year Four	840	340
Year Five	324	82
Year Six and Prior	708	646
Revolving	1,455	1,622
Total	3,821	3,857
Consumer | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	481
Year Two	546	959
Year Three	739	1,884
Year Four	1,423	500
Year Five	386	897
Year Six and Prior	2,499	1,976
Revolving	820	822
Total	$ 6,413	$ 7,519