Shareholders' Equity, Compliance with Regulatory Capital Requirements (Details) $ in Thousands	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
CET1 capital to risk-weighted assets [Abstract]
Actual Amount	$ 450,687	$ 395,941
Minimum Capital Requirement, Amount	$ 173,674	$ 161,178
CET1 capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1168	0.1105
Minimum Capital Requirement, Ratio	0.0450	0.0450
Tier 1 capital to risk-weighted assets [Abstract]
Actual Amount	$ 460,687	$ 405,941
Minimum Capital Requirement, Amount	$ 231,566	$ 214,904
Tier 1 capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1194	0.1133
Minimum Capital Requirement, Ratio	0.0600	0.0600
Risk-based capital to risk-weighted assets [Abstract]
Actual Amount	$ 509,091	$ 450,890
Minimum Capital Requirement, Amount	$ 308,755	$ 286,539
Risk-based capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1319	0.1259
Minimum Capital Requirement, Ratio	0.0800	0.0800
Tier 1 leverage capital ratio [Abstract]
Actual Amount	$ 460,687	$ 405,941
Minimum Capital Requirement, Amount	$ 206,606	$ 177,820
Tier 1 leverage capital ratio, Ratio [Abstract]
Actual Ratio	0.0892	0.0913
Minimum Capital Requirement, Ratio	0.0400	0.0400
Farmers & Merchants Bank [Member]
CET1 capital to risk-weighted assets [Abstract]
Actual Amount	$ 459,813	$ 401,313
Minimum Capital Requirement, Amount	173,664	161,135
Well Capitalized Requirement, Amount	$ 250,847	$ 232,750
CET1 capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1191	0.1121
Minimum Capital Requirement, Ratio	0.0450	0.0450
Well Capitalized Requirement, Ratio	0.0650	0.0650
Tier 1 capital to risk-weighted assets [Abstract]
Actual Amount	$ 459,813	$ 401,313
Minimum Capital Requirement, Amount	231,551	214,846
Well Capitalized Requirement, Amount	$ 308,735	$ 286,462
Tier 1 capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1191	0.1121
Minimum Capital Requirement, Ratio	0.0600	0.0600
Well Capitalized Requirement, Ratio	0.0800	0.0800
Risk-based capital to risk-weighted assets [Abstract]
Actual Amount	$ 508,215	$ 446,251
Minimum Capital Requirement, Amount	308,735	286,462
Well Capitalized Requirement, Amount	$ 385,919	$ 358,077
Risk-based capital to risk-weighted assets, Ratio [Abstract]
Actual Ratio	0.1317	0.1246
Minimum Capital Requirement, Ratio	0.0800	0.0800
Well Capitalized Requirement, Ratio	0.1000	0.1000
Tier 1 leverage capital ratio [Abstract]
Actual Amount	$ 459,813	$ 401,313
Minimum Capital Requirement, Amount	206,426	177,605
Well Capitalized Requirement, Amount	$ 258,033	$ 222,006
Tier 1 leverage capital ratio, Ratio [Abstract]
Actual Ratio	0.0891	0.0904
Minimum Capital Requirement, Ratio	0.0400	0.0400
Well Capitalized Requirement, Ratio	0.0500	0.0500