Loans - Allowance For Credit Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for loan losses:
Beginning balance	$ 26,530	$ 26,510	$ 24,020
Charge-offs	(2,104)	(2,631)	(3,405)
Recoveries	3,286	3,814	4,240
Provision	1,688	(1,163)	1,655
Ending balance	29,400	26,530	26,510
Ending balance, individually evaluated for impairment	2,166	2,343	883
Ending balance, collectively evaluated for impairment	27,234	24,187	25,627
Loan balances:
Ending balance	2,459,671	2,277,148	2,124,916
Ending balance, individually evaluated for impairment	31,487	33,664	16,261
Ending balance, collectively evaluated for impairment	2,428,184	2,243,484	2,108,655
Agricultural [Member]
Allowance for loan losses:
Beginning balance	2,947	3,082	2,515
Charge-offs	(167)	(226)	(325)
Recoveries	146	181	123
Provision	(632)	(90)	769
Ending balance	2,294	2,947	3,082
Ending balance, individually evaluated for impairment	133	856	1
Ending balance, collectively evaluated for impairment	2,161	2,091	3,081
Loan balances:
Ending balance	88,580	92,871	101,588
Ending balance, individually evaluated for impairment	4,916	11,720	1,710
Ending balance, collectively evaluated for impairment	83,664	81,151	99,878
Commercial and Financial [Member]
Allowance for loan losses:
Beginning balance	4,531	4,517	4,231
Charge-offs	(583)	(315)	(526)
Recoveries	1,183	1,169	1,370
Provision	(294)	(840)	(558)
Ending balance	4,837	4,531	4,517
Ending balance, individually evaluated for impairment	1,018	718	324
Ending balance, collectively evaluated for impairment	3,819	3,813	4,193
Loan balances:
Ending balance	218,632	192,995	184,199
Ending balance, individually evaluated for impairment	2,768	2,477	2,110
Ending balance, collectively evaluated for impairment	215,864	190,518	182,089
Real Estate: Construction and land development [Member]
Allowance for loan losses:
Beginning balance	2,890	2,280	2,241
Charge-offs	(114)	(34)	(285)
Recoveries	662	849	501
Provision	(449)	(205)	(177)
Ending balance	2,989	2,890	2,280
Ending balance, individually evaluated for impairment	39	105	22
Ending balance, collectively evaluated for impairment	2,950	2,785	2,258
Loan balances:
Ending balance	179,333	179,425	134,467
Ending balance, individually evaluated for impairment	957	1,136	954
Ending balance, collectively evaluated for impairment	178,376	178,289	133,513
Real Estate: Mortgage, farmland [Member]
Allowance for loan losses:
Beginning balance	3,417	3,342	2,672
Charge-offs	(3)	(116)	0
Recoveries	0	0	6
Provision	255	191	664
Ending balance	3,669	3,417	3,342
Ending balance, individually evaluated for impairment	238	390	0
Ending balance, collectively evaluated for impairment	3,431	3,027	3,342
Loan balances:
Ending balance	215,286	202,340	187,856
Ending balance, individually evaluated for impairment	7,962	8,028	2,233
Ending balance, collectively evaluated for impairment	207,324	194,312	185,623
Real Estate: Mortgage, 1 to 4 family [Member]
Allowance for loan losses:
Beginning balance	7,677	8,172	7,419
Charge-offs	(553)	(1,181)	(1,108)
Recoveries	661	1,043	762
Provision	883	(357)	1,099
Ending balance	8,668	7,677	8,172
Ending balance, individually evaluated for impairment	66	90	326
Ending balance, collectively evaluated for impairment	8,602	7,587	7,846
Loan balances:
Ending balance	975,791	892,869	845,033
Ending balance, individually evaluated for impairment	6,654	7,042	5,926
Ending balance, collectively evaluated for impairment	969,137	885,827	839,107
Real Estate: Mortgage, multi-family and commercial [Member]
Allowance for loan losses:
Beginning balance	4,045	4,223	4,195
Charge-offs	(130)	(66)	(723)
Recoveries	376	385	1,310
Provision	1,409	(497)	(559)
Ending balance	5,700	4,045	4,223
Ending balance, individually evaluated for impairment	482	34	110
Ending balance, collectively evaluated for impairment	5,218	4,011	4,113
Loan balances:
Ending balance	698,006	637,029	595,383
Ending balance, individually evaluated for impairment	8,040	3,111	3,228
Ending balance, collectively evaluated for impairment	689,966	633,918	592,155
Others [Member]
Allowance for loan losses:
Beginning balance	1,023	894	747
Charge-offs	(554)	(693)	(438)
Recoveries	258	187	168
Provision	516	635	417
Ending balance	1,243	1,023	894
Ending balance, individually evaluated for impairment	190	150	100
Ending balance, collectively evaluated for impairment	1,053	873	794
Loan balances:
Ending balance	84,043	79,619	76,390
Ending balance, individually evaluated for impairment	190	150	100
Ending balance, collectively evaluated for impairment	$ 83,853	$ 79,469	$ 76,290