LOANS (Past due financing receivables) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 24,408	$ 16,650
Current	7,751,258	7,322,288
Nonaccrual	79,619	71,943
Total	7,855,285	7,410,881
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	20,219	15,363
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	3,904	561
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	285	726
Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	13,248	8,324
Current	6,175,339	5,685,784
Nonaccrual	41,785	37,604
Total	6,230,372	5,731,712
Commercial | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	10,961	7,393
Commercial | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	2,287	205
Commercial | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	726
Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	7,311	2,779
Current	2,205,913	1,991,525
Nonaccrual	25,229	25,927
Total	2,238,453	2,020,231
Commercial | Commercial | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	6,030	2,574
Commercial | Commercial | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,281	205
Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Commercial | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	5,937	5,545
Current	3,969,426	3,694,259
Nonaccrual	16,556	11,677
Total	3,991,919	3,711,481
Commercial | Commercial real estate | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	4,931	4,819
Commercial | Commercial real estate | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,006	0
Commercial | Commercial real estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	726
Agricultural and agricultural real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	3,335	99
Current	524,655	549,376
Nonaccrual	21,414	15,933
Total	549,404	565,408
Agricultural and agricultural real estate | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	2,664	99
Agricultural and agricultural real estate | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	386	0
Agricultural and agricultural real estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	285	0
Residential real estate
Financing Receivable, Past Due [Line Items]
Total Past Due	3,397	5,196
Current	598,120	655,329
Nonaccrual	12,190	13,078
Total	613,707	673,603
Residential real estate | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	2,744	5,147
Residential real estate | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	653	49
Residential real estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	4,428	3,031
Current	453,144	431,799
Nonaccrual	4,230	5,328
Total	461,802	440,158
Consumer | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	3,850	2,724
Consumer | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	578	307
Consumer | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 0	$ 0