Parent Company Financial Information, Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Balance Sheets [Abstract]
Investment Securities	$ 536,056	$ 506,372
Total Assets	3,075,452	2,922,121
Subordinated Debentures	10,310	10,310
Liabilities	2,775,792	2,642,140
Shareholders' Equity	299,660	279,981	$ 251,835	$ 233,178
Total Liabilities and Shareholders' Equity	3,075,452	2,922,121
Parent Company [Member]
Condensed Balance Sheets [Abstract]
Cash	332	228	$ 308	$ 363
Investment in Farmers & Merchants Bank of Central California	297,643	289,778
Investment Securities	409	409
Other Assets	12,006	184
Total Assets	310,390	290,599
Subordinated Debentures	10,310	10,310
Liabilities	420	308
Shareholders' Equity	299,660	279,981
Total Liabilities and Shareholders' Equity	$ 310,390	$ 290,599