Shareholders' Equity, Compliance with Regulatory Capital Requirements (Details) $ in Thousands	Sep. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
CET1 capital to risk-weighted assets [Abstract]
Actual Amount	$ 482,053	$ 450,687
Minimum to be Categorized as "Adequately Capitalized", Amount	$ 183,537	$ 173,674
CET1 capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1182	0.1168
Minimum to be Categorized as "Adequately Capitalized", Ratio	0.045	0.045
Tier 1 capital to risk-weighted assets [Abstract]
Actual Amount	$ 492,053	$ 460,687
Minimum Capital Requirement, Amount	$ 244,716	$ 231,566
Tier 1 capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1206	0.1194
Minimum Capital Requirement, Ratio	0.06	0.06
Risk-based capital to risk-weighted assets [Abstract]
Actual Amount	$ 543,218	$ 509,091
Minimum Capital Requirement, Amount	$ 326,288	$ 308,755
Risk-based capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1332	0.1319
Minimum Capital Requirement, Ratio	0.08	0.08
Tier 1 leverage capital ratio [Abstract]
Actual Amount	$ 492,053	$ 460,687
Minimum Capital Requirement, Amount	$ 215,702	$ 206,606
Tier 1 leverage capital ratio, Ratio [Abstract]
Actual Ratio	0.0912	0.0892
Minimum Capital Requirement, Ratio	0.04	0.04
Farmers & Merchants Bank [Member]
CET1 capital to risk-weighted assets [Abstract]
Actual Amount	$ 491,237	$ 459,813
Minimum to be Categorized as "Adequately Capitalized", Amount	183,531	173,664
Minimum to be Categorized as "Well Capitalized", Amount	$ 265,101	$ 250,847
CET1 capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1204	0.1191
Minimum to be Categorized as "Adequately Capitalized", Ratio	0.045	0.045
Minimum to be Categorized as "Well Capitalized", Ratio	0.065	0.065
Tier 1 capital to risk-weighted assets [Abstract]
Actual Amount	$ 491,237	$ 459,813
Minimum Capital Requirement, Amount	244,708	231,551
Well Capitalized Requirement, Amount	$ 326,278	$ 308,735
Tier 1 capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1204	0.1191
Minimum Capital Requirement, Ratio	0.06	0.06
Well Capitalized Requirement, Ratio	0.08	0.08
Risk-based capital to risk-weighted assets [Abstract]
Actual Amount	$ 542,400	$ 508,215
Minimum Capital Requirement, Amount	326,278	308,735
Well Capitalized Requirement, Amount	$ 407,847	$ 385,919
Risk-based capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.133	0.1317
Minimum Capital Requirement, Ratio	0.08	0.08
Well Capitalized Requirement, Ratio	0.10	0.10
Tier 1 leverage capital ratio [Abstract]
Actual Amount	$ 491,237	$ 459,813
Minimum Capital Requirement, Amount	215,498	206,426
Well Capitalized Requirement, Amount	$ 269,372	$ 258,033
Tier 1 leverage capital ratio, Ratio [Abstract]
Actual Ratio	0.0912	0.0891
Minimum Capital Requirement, Ratio	0.04	0.04
Well Capitalized Requirement, Ratio	0.05	0.05

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
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-URI https://asc.fasb.org/extlink&oid=117337116&loc=SL5958570-112826

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