Allowance for Probable Loan Losses (Impaired Loans) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Interest Recognized
Total trouble debt restructuring	$ 7,839		$ 7,839	$ 8,158
Period of charge off for past due unsecured commercial loans	90 days		90 days
Class of Financing Receivable
Recorded investment:
Total impaired loans with related allowance	$ 726	$ 1,936	$ 726	1,698
Total impaired loans with no related allowance	19,263	65,134	19,263	22,202
Unpaid principal balance:
Total impaired loans with an allowance recorded	790		790	2,330
Total impaired loans with no related allowance recorded	20,480	276	20,480	23,284
Related Allowance	511		511	772
Average recorded investment:
Total impaired loans with an allowance recorded	731	1,759	748	1,882
Total impaired loans with no related allowance recorded	22,297	32,938	51,852	65,192
Interest Recognized
Total impaired loans with no related allowance recorded	92	92	274	368
Commercial
Interest Recognized
Total trouble debt restructuring	33		33	35
Commercial \| Class of Financing Receivable
Recorded investment:
Total impaired loans with related allowance	598	1,794	598	1,563
Total impaired loans with no related allowance	6,814	16,464	6,814	7,616
Unpaid principal balance:
Total impaired loans with an allowance recorded	621		621	2,161
Total impaired loans with no related allowance recorded	6,963	2	6,963	7,730
Related Allowance	395		395	656
Average recorded investment:
Total impaired loans with an allowance recorded	602	1,620	616	1,741
Total impaired loans with no related allowance recorded	8,002	15,758	17,945	16,194
Interest Recognized
Total impaired loans with no related allowance recorded	1		2	3
Commercial Real Estate:Other Construction and Land Development \| Class of Financing Receivable
Recorded investment:
Total impaired loans with related allowance	128	142	128	135
Total impaired loans with no related allowance	1,666	2,203	1,666	1,957
Unpaid principal balance:
Total impaired loans with an allowance recorded	169		169	169
Total impaired loans with no related allowance recorded	1,953		1,953	2,205
Related Allowance	116		116	116
Average recorded investment:
Total impaired loans with an allowance recorded	129	139	132	141
Total impaired loans with no related allowance recorded	1,674	1,994	1,767	2,151
Commercial Real Estate: Farmland and Commercial \| Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance	1,740	36,633	1,740	3,509
Unpaid principal balance:
Total impaired loans with no related allowance recorded	2,368		2,368	4,031
Average recorded investment:
Total impaired loans with no related allowance recorded	3,222	5,986	22,389	36,632
Commercial Real Estate: Multifamily \| Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance	649	575	649	507
Unpaid principal balance:
Total impaired loans with no related allowance recorded	684		684	538
Average recorded investment:
Total impaired loans with no related allowance recorded	653	590	656	565
Residential First Lien
Interest Recognized
Total trouble debt restructuring	5,703		5,703	5,947
Residential First Lien \| Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance	6,286	6,929	6,286	6,244
Unpaid principal balance:
Total impaired loans with no related allowance recorded	6,400	228	6,400	6,386
Average recorded investment:
Total impaired loans with no related allowance recorded	6,427	6,362	6,698	7,136
Interest Recognized
Total impaired loans with no related allowance recorded	78	76	231	305
Residential Junior Lien
Interest Recognized
Total trouble debt restructuring	704		704	730
Residential Junior Lien \| Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance	704	807	704	901
Unpaid principal balance:
Total impaired loans with no related allowance recorded	708	33	708	911
Average recorded investment:
Total impaired loans with no related allowance recorded	914	743	1,028	976
Interest Recognized
Total impaired loans with no related allowance recorded	10	11	32	44
Consumer
Interest Recognized
Total trouble debt restructuring	1,126		1,126	1,153
Consumer \| Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance	1,131	1,192	1,131	1,175
Unpaid principal balance:
Total impaired loans with no related allowance recorded	1,131	2	1,131	1,190
Average recorded investment:
Total impaired loans with no related allowance recorded	1,131	1,187	1,088	1,211
Interest Recognized
Total impaired loans with no related allowance recorded		1		2
Foreign
Interest Recognized
Total trouble debt restructuring	273		273	293
Foreign \| Class of Financing Receivable
Recorded investment:
Total impaired loans with no related allowance	273	331	273	293
Unpaid principal balance:
Total impaired loans with no related allowance recorded	273	11	273	293
Average recorded investment:
Total impaired loans with no related allowance recorded	274	318	281	327
Interest Recognized
Total impaired loans with no related allowance recorded	$ 3	$ 4	$ 9	$ 14

Amount of financing receivable modified as troubled debt restructuring.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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