Loans - Impaired Financing Receivables Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Recorded Investment
With no related allowance recorded	$ 14,356	$ 12,563	$ 11,288
With a related allowance recorded	17,131	21,101	4,973
Total	31,487	33,664	16,261
Unpaid Principal Balance
With no related allowance recorded	18,735	16,365	14,840
With a related allowance recorded	17,202	21,377	5,355
Total	35,937	37,742	20,195
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	2,166	2,343	883
Total	2,166	2,343	883
Average Recorded Investment
With no related allowance recorded	15,306	13,425	11,774
With an related allowance recorded	17,810	21,163	5,272
Total	33,116	34,588	17,046
Interest Income Recognized
With no related allowance recorded	270	195	304
With an related allowance recorded	802	880	126
Total	1,072	1,075	430
Agricultural [Member]
Recorded Investment
With no related allowance recorded	1,822	800	1,609
With a related allowance recorded	3,094	10,920	101
Total	4,916	11,720	1,710
Unpaid Principal Balance
With no related allowance recorded	2,193	971	1,773
With a related allowance recorded	3,149	10,978	101
Total	5,342	11,949	1,874
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	133	856	1
Total	133	856	1
Average Recorded Investment
With no related allowance recorded	2,044	923	1,620
With an related allowance recorded	3,526	11,258	106
Total	5,570	12,181	1,726
Interest Income Recognized
With no related allowance recorded	19	0	80
With an related allowance recorded	160	464	5
Total	179	464	85
Commercial and financial [Member]
Recorded Investment
With no related allowance recorded	1,725	1,540	1,263
With a related allowance recorded	1,043	937	847
Total	2,768	2,477	2,110
Unpaid Principal Balance
With no related allowance recorded	2,487	2,175	1,981
With a related allowance recorded	1,043	955	847
Total	3,530	3,130	2,828
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	1,018	718	324
Total	1,018	718	324
Average Recorded Investment
With no related allowance recorded	2,080	1,662	1,421
With an related allowance recorded	1,249	777	990
Total	3,329	2,439	2,411
Interest Income Recognized
With no related allowance recorded	51	18	5
With an related allowance recorded	60	27	30
Total	111	45	35
Construction, 1 to 4 family residential [Member]
Recorded Investment
With no related allowance recorded	114	117	238
With a related allowance recorded	0	815	449
Total	114	932	687
Unpaid Principal Balance
With no related allowance recorded	150	151	238
With a related allowance recorded	0	815	461
Total	150	966	699
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	0	105	9
Total	0	105	9
Average Recorded Investment
With no related allowance recorded	116	131	173
With an related allowance recorded	0	537	449
Total	116	668	622
Interest Income Recognized
With no related allowance recorded	5	6	5
With an related allowance recorded	0	27	12
Total	5	33	17
Construction, land development and commercial [Member]
Recorded Investment
With no related allowance recorded	338	204	210
With a related allowance recorded	505	0	57
Total	843	204	267
Unpaid Principal Balance
With no related allowance recorded	371	290	314
With a related allowance recorded	505	0	58
Total	876	290	372
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	39	0	13
Total	39	0	13
Average Recorded Investment
With no related allowance recorded	344	207	231
With an related allowance recorded	321	0	58
Total	665	207	289
Interest Income Recognized
With no related allowance recorded	14	5	6
With an related allowance recorded	14	0	0
Total	28	5	6
Mortgage, farmland [Member]
Recorded Investment
With no related allowance recorded	2,523	2,594	2,233
With a related allowance recorded	5,439	5,434	0
Total	7,962	8,028	2,233
Unpaid Principal Balance
With no related allowance recorded	2,902	2,887	2,351
With a related allowance recorded	5,439	5,434	0
Total	8,341	8,321	2,351
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	238	390	0
Total	238	390	0
Average Recorded Investment
With no related allowance recorded	2,476	2,767	2,305
With an related allowance recorded	5,596	5,591	0
Total	8,072	8,358	2,305
Interest Income Recognized
With no related allowance recorded	56	67	110
With an related allowance recorded	242	240	0
Total	298	307	110
Mortgage, 1 to 4 family first liens [Member]
Recorded Investment
With no related allowance recorded	6,045	5,011	3,558
With a related allowance recorded	577	1,266	2,062
Total	6,622	6,277	5,620
Unpaid Principal Balance
With no related allowance recorded	7,507	6,137	4,419
With a related allowance recorded	593	1,374	2,156
Total	8,100	7,511	6,575
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	63	79	306
Total	63	79	306
Average Recorded Investment
With no related allowance recorded	6,286	5,265	3,806
With an related allowance recorded	585	1,226	2,133
Total	6,871	6,491	5,939
Interest Income Recognized
With no related allowance recorded	80	53	48
With an related allowance recorded	20	43	36
Total	100	96	84
Mortgage, 1 to 4 family junior liens [Member]
Recorded Investment
With no related allowance recorded	7	153	189
With a related allowance recorded	25	612	117
Total	32	765	306
Unpaid Principal Balance
With no related allowance recorded	482	646	500
With a related allowance recorded	25	667	270
Total	507	1,313	770
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	3	11	20
Total	3	11	20
Average Recorded Investment
With no related allowance recorded	23	186	204
With an related allowance recorded	26	637	179
Total	49	823	383
Interest Income Recognized
With no related allowance recorded	0	0	0
With an related allowance recorded	1	27	1
Total	1	27	1
Mortgage, multi-family [Member]
Recorded Investment
With no related allowance recorded	218	243	157
With a related allowance recorded	6,179	0	292
Total	6,397	243	449
Unpaid Principal Balance
With no related allowance recorded	355	362	226
With a related allowance recorded	6,179	0	332
Total	6,534	362	558
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	480	0	58
Total	480	0	58
Average Recorded Investment
With no related allowance recorded	231	288	175
With an related allowance recorded	6,247	0	316
Total	6,478	288	491
Interest Income Recognized
With no related allowance recorded	0	0	0
With an related allowance recorded	281	0	0
Total	281	0	0
Real Estate: Mortgage, commercial [Member]
Recorded Investment
With no related allowance recorded	1,564	1,901	1,831
With a related allowance recorded	79	967	948
Total	1,643	2,868	2,779
Unpaid Principal Balance
With no related allowance recorded	2,274	2,727	3,018
With a related allowance recorded	79	1,004	1,030
Total	2,353	3,731	4,048
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	2	34	52
Total	2	34	52
Average Recorded Investment
With no related allowance recorded	1,706	1,996	1,839
With an related allowance recorded	81	986	974
Total	1,787	2,982	2,813
Interest Income Recognized
With no related allowance recorded	45	46	50
With an related allowance recorded	4	36	38
Total	49	82	88
Loans to individuals [Member]
Recorded Investment
With no related allowance recorded	0	0	0
With a related allowance recorded	190	150	100
Total	190	150	100
Unpaid Principal Balance
With no related allowance recorded	14	19	20
With a related allowance recorded	190	150	100
Total	204	169	120
Related Allowance
With no related allowance recorded	0	0	0
With an related allowance recorded	190	150	100
Total	190	150	100
Average Recorded Investment
With no related allowance recorded	0	0	0
With an related allowance recorded	179	151	67
Total	179	151	67
Interest Income Recognized
With no related allowance recorded	0	0	0
With an related allowance recorded	20	16	4
Total	$ 20	$ 16	$ 4