LOANS AND ALLOWANCE FOR LOAN LOSSES - Risk Categories of Loans by Class of Loans - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Risk category of loans
Loans	$ 3,063,463	$ 2,651,673
Purchases	427,541	355,343
Sales	243,179	256,946
Pass
Risk category of loans
Loans	1,796,110	1,481,038
Special Mention
Risk category of loans
Loans	32,033	20,526
Substandard
Risk category of loans
Loans	20,066	18,626
Non-accrual
Risk category of loans
Loans	7,279	5,844
Substandard Commercial
Risk category of loans
Loans	665	1,421
Performing
Risk category of loans
Loans	160,261	169,710
Watch
Risk category of loans
Loans	52	90
Commercial
Risk category of loans
Loans	578,991	534,559
Purchases	12,281	14,241
Commercial | Commercial and industrial
Risk category of loans
Loans	515,122	461,092
Commercial | Commercial and industrial | Pass
Risk category of loans
Loans	468,610	415,064
Commercial | Commercial and industrial | Special Mention
Risk category of loans
Loans	3,786	3,347
Commercial | Commercial and industrial | Substandard
Risk category of loans
Loans	2,340	5,297
Commercial | Commercial and industrial | Non-accrual
Risk category of loans
Loans	1,885	827
Commercial | Commercial and industrial | Substandard Commercial
Risk category of loans
Loans	5	55
Commercial | Commercial and industrial | Performing
Risk category of loans
Loans	38,490	36,502
Commercial | Commercial and industrial | Watch
Risk category of loans
Loans	6
Commercial | Agricultural
Risk category of loans
Loans	63,869	73,467
Commercial | Agricultural | Pass
Risk category of loans
Loans	53,271	61,637
Commercial | Agricultural | Special Mention
Risk category of loans
Loans	1,556	2,283
Commercial | Agricultural | Substandard
Risk category of loans
Loans	369
Commercial | Agricultural | Non-accrual
Risk category of loans
Loans	1,438	1,441
Commercial | Agricultural | Substandard Commercial
Risk category of loans
Loans	33	190
Commercial | Agricultural | Performing
Risk category of loans
Loans	7,202	7,916
Commercial real estate
Risk category of loans
Loans	1,437,475	1,162,696
Purchases	304,702	138,896
Commercial real estate | Farm
Risk category of loans
Loans	106,010	111,807
Commercial real estate | Farm | Pass
Risk category of loans
Loans	85,763	89,297
Commercial real estate | Farm | Special Mention
Risk category of loans
Loans	3,055	2,209
Commercial real estate | Farm | Substandard
Risk category of loans
Loans	1,536	694
Commercial real estate | Farm | Non-accrual
Risk category of loans
Loans	857	1,340
Commercial real estate | Farm | Substandard Commercial
Risk category of loans
Loans	4	7
Commercial real estate | Farm | Performing
Risk category of loans
Loans	14,795	18,260
Commercial real estate | Hotel
Risk category of loans
Loans	119,512	91,213
Commercial real estate | Hotel | Pass
Risk category of loans
Loans	119,512	88,166
Commercial real estate | Hotel | Substandard
Risk category of loans
Loans		2,983
Commercial real estate | Hotel | Non-accrual
Risk category of loans
Loans		64
Commercial real estate | Construction and development
Risk category of loans
Loans	86,045	102,598
Commercial real estate | Construction and development | Pass
Risk category of loans
Loans	65,825	74,811
Commercial real estate | Construction and development | Special Mention
Risk category of loans
Loans		3,600
Commercial real estate | Construction and development | Substandard
Risk category of loans
Loans	1,613	2,287
Commercial real estate | Construction and development | Non-accrual
Risk category of loans
Loans		31
Commercial real estate | Construction and development | Substandard Commercial
Risk category of loans
Loans		91
Commercial real estate | Construction and development | Performing
Risk category of loans
Loans	18,607	21,778
Commercial real estate | Other
Risk category of loans
Loans	1,125,908	857,078
Commercial real estate | Other | Pass
Risk category of loans
Loans	1,003,129	752,063
Commercial real estate | Other | Special Mention
Risk category of loans
Loans	23,636	9,087
Commercial real estate | Other | Substandard
Risk category of loans
Loans	14,208	7,365
Commercial real estate | Other | Non-accrual
Risk category of loans
Loans	3,099	2,141
Commercial real estate | Other | Substandard Commercial
Risk category of loans
Loans	623	1,078
Commercial real estate | Other | Performing
Risk category of loans
Loans	81,167	85,254
Commercial real estate | Other | Watch
Risk category of loans
Loans	46	90
Residential
Risk category of loans
Loans	980,171	892,513
Purchases	109,300	201,397
Sales	243,179	256,946
Residential | Substandard
Risk category of loans
Loans	3,626	4,176
Residential | Performing
Risk category of loans
Loans	974,178	886,198
Residential | Watch
Risk category of loans
Loans	2,367	2,139
Residential | 1-4 family
Risk category of loans
Loans	681,518	608,366
Residential | 1-4 family | Substandard
Risk category of loans
Loans	3,239	3,262
Residential | 1-4 family | Performing
Risk category of loans
Loans	676,176	603,102
Residential | 1-4 family | Watch
Risk category of loans
Loans	2,103	2,002
Residential | Home equity
Risk category of loans
Loans	298,653	284,147
Residential | Home equity | Substandard
Risk category of loans
Loans	387	914
Residential | Home equity | Performing
Risk category of loans
Loans	298,002	283,096
Residential | Home equity | Watch
Risk category of loans
Loans	264	137
Consumer
Risk category of loans
Loans	66,826	61,905
Purchases	1,258	809
Consumer | Substandard
Risk category of loans
Loans		4
Consumer | Performing
Risk category of loans
Loans	65,875	61,839
Consumer | Loss
Risk category of loans
Loans	951	62
Consumer | Direct
Risk category of loans
Loans	66,658	61,574
Consumer | Direct | Substandard
Risk category of loans
Loans		4
Consumer | Direct | Performing
Risk category of loans
Loans	65,707	61,508
Consumer | Direct | Loss
Risk category of loans
Loans	951	62
Consumer | Indirect
Risk category of loans
Loans	168	331
Consumer | Indirect | Performing
Risk category of loans
Loans	$ 168	$ 331
Minimum | Substandard
Risk category of loans
Period of loans past due	90 days
Minimum | Non-accrual
Risk category of loans
Period for which principal and interest has been in default	90 days
Minimum | Watch
Risk category of loans
Period of loans past due	60 days
Minimum | Loss
Risk category of loans
Period of loans past due	119 days
Minimum | Consumer loans not secured by 1-4 family residential real estate | Substandard
Risk category of loans
Period of loans past due	60 days
Maximum | Watch
Risk category of loans
Period of loans past due	89 days
Maximum | Consumer loans not secured by 1-4 family residential real estate | Substandard
Risk category of loans
Period of loans past due	119 days