LOANS AND ALLOWANCE - Nonaccrual and loans past due over 90 days still on accrual by class of loans - (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	$ 3,047,250	$ 2,651,673
Total Past Due	16,868	23,234
Loans Not Past Due	3,030,382	2,628,439
30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,267	9,640
60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,503	2,229
Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	12,098	11,365
Commercial
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	559,995	534,559
Commercial | Commercial and industrial
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	496,523	461,092
Total Past Due	2,491	176
Loans Not Past Due	494,032	460,916
Commercial | Commercial and industrial | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	274
Commercial | Commercial and industrial | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	389
Commercial | Commercial and industrial | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	1,828	176
Commercial | Agricultural
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	63,472	73,467
Total Past Due	1,530	1,821
Loans Not Past Due	61,942	71,646
Commercial | Agricultural | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	34	215
Commercial | Agricultural | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	1,496	1,606
Commercial real estate
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	1,425,275	1,162,696
Commercial real estate | Farm
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	103,783	111,807
Total Past Due	1,564	1,324
Loans Not Past Due	102,219	110,483
Commercial real estate | Farm | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	5	81
Commercial real estate | Farm | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	1,559	1,243
Commercial real estate | Hotel
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	120,829	91,213
Total Past Due		63
Loans Not Past Due	120,829	91,150
Commercial real estate | Hotel | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due		63
Commercial real estate | Construction and development
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	98,906	102,598
Total Past Due	9	3,639
Loans Not Past Due	98,897	98,959
Commercial real estate | Construction and development | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	9	1,416
Commercial real estate | Construction and development | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due		2,223
Commercial real estate | Other
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	1,101,757	857,078
Total Past Due	3,511	3,170
Loans Not Past Due	1,098,246	853,908
Commercial real estate | Other | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	369	1,268
Commercial real estate | Other | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	12	90
Commercial real estate | Other | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	3,130	1,812
Residential
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	995,495	892,513
Residential | 1-4 family
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	694,163	608,366
Total Past Due	5,490	10,148
Loans Not Past Due	688,673	598,218
Residential | 1-4 family | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	934	4,884
Residential | 1-4 family | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	1,965	2,002
Residential | 1-4 family | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,591	3,262
Residential | Home equity
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	301,332	284,147
Total Past Due	1,191	1,881
Loans Not Past Due	300,141	282,266
Residential | Home equity | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	485	830
Residential | Home equity | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	126	137
Residential | Home equity | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	580	914
Consumer
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	66,485	61,905
Consumer | Direct
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	66,281	61,574
Total Past Due	1,082	1,002
Loans Not Past Due	65,199	60,572
Consumer | Direct | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	157	936
Consumer | Direct | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	11
Consumer | Direct | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	914	66
Consumer | Indirect
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	204	331
Total Past Due		10
Loans Not Past Due	$ 204	321
Consumer | Indirect | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due		$ 10