LOANS AND ALLOWANCE FOR LOAN LOSSES- Nonaccrual and loans past due over 90 days still on accrual by class of loans - (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Interest Receivable	$ 9,095	$ 7,342
Aging of the recorded investment in past due loans
Total	3,063,463	2,651,673
Total Past Due	21,936	23,234
Loans Not Past Due	3,041,527	2,628,439
30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	8,130	9,640
60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,636	2,229
Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	11,170	11,365
Commercial
Aging of the recorded investment in past due loans
Total	578,991	534,559
Commercial | Commercial and industrial
Aging of the recorded investment in past due loans
Total	515,122	461,092
Total Past Due	2,619	176
Loans Not Past Due	512,503	460,916
Commercial | Commercial and industrial | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	723
Commercial | Commercial and industrial | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	6
Commercial | Commercial and industrial | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	1,890	176
Commercial | Agricultural
Aging of the recorded investment in past due loans
Total	63,869	73,467
Total Past Due	1,472	1,821
Loans Not Past Due	62,397	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	1,438	1,606
Commercial real estate
Aging of the recorded investment in past due loans
Total	1,437,475	1,162,696
Commercial real estate | Farm
Aging of the recorded investment in past due loans
Total	106,010	111,807
Total Past Due	787	1,324
Loans Not Past Due	105,223	110,483
Commercial real estate | Farm | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	4	81
Commercial real estate | Farm | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	783	1,243
Commercial real estate | Hotel
Aging of the recorded investment in past due loans
Total	119,512	91,213
Total Past Due		63
Loans Not Past Due	119,512	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	86,045	102,598
Total Past Due		3,639
Loans Not Past Due	86,045	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		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	1,125,908	857,078
Total Past Due	3,751	3,170
Loans Not Past Due	1,122,157	853,908
Commercial real estate | Other | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	983	1,268
Commercial real estate | Other | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	263	90
Commercial real estate | Other | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,505	1,812
Residential
Aging of the recorded investment in past due loans
Total	980,171	892,513
Residential | 1-4 family
Aging of the recorded investment in past due loans
Total	681,518	608,366
Total Past Due	11,045	10,148
Loans Not Past Due	670,473	598,218
Residential | 1-4 family | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	5,703	4,884
Residential | 1-4 family | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,103	2,002
Residential | 1-4 family | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	3,239	3,262
Residential | Home equity
Aging of the recorded investment in past due loans
Total	298,653	284,147
Total Past Due	1,204	1,881
Loans Not Past Due	297,449	282,266
Residential | Home equity | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	553	830
Residential | Home equity | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	264	137
Residential | Home equity | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	387	914
Consumer
Aging of the recorded investment in past due loans
Total	66,826	61,905
Consumer | Direct
Aging of the recorded investment in past due loans
Total	66,658	61,574
Total Past Due	1,058	1,002
Loans Not Past Due	65,600	60,572
Consumer | Direct | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	130	936
Consumer | Direct | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	928	66
Consumer | Indirect
Aging of the recorded investment in past due loans
Total	168	331
Total Past Due		10
Loans Not Past Due	$ 168	321
Consumer | Indirect | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due		$ 10