Parent Company Financial Information, Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Balance Sheets [Abstract]
Investment Securities	$ 876,665	$ 567,615
Total Assets	4,550,453	3,721,830
Subordinated Debentures	10,310	10,310
Liabilities	4,126,788	3,352,534
Shareholders' Equity	423,665	369,296	$ 311,215	$ 299,660
Total Liabilities and Shareholders' Equity	4,550,453	3,721,830
Parent Company [Member]
Condensed Balance Sheets [Abstract]
Cash	4,551	1,341	$ 335	$ 332
Investment in Farmers & Merchants Bank of Central California	429,037	378,271
Investment Securities	434	411
Other Assets	832	102
Total Assets	434,854	380,125
Subordinated Debentures	10,310	10,310
Liabilities	879	519
Shareholders' Equity	423,665	369,296
Total Liabilities and Shareholders' Equity	$ 434,854	$ 380,125