Parent Company Financial Information, Condensed Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Statements of Income [Abstract]
Interest Income	$ 40,621	$ 37,699	$ 35,415	$ 35,426	$ 35,654	$ 35,280	$ 35,373	$ 34,207	$ 149,161	$ 140,514	$ 125,503
Tax Benefit	(5,298)	(4,945)	(4,533)	(4,441)	(5,037)	(4,660)	(4,903)	(4,677)	(19,217)	(19,277)	(14,203)
Net Income	$ 15,493	$ 14,810	$ 14,309	$ 14,122	$ 14,644	$ 13,738	$ 14,105	$ 13,549	58,734	56,036	45,527
Parent Company [Member]
Condensed Statements of Income [Abstract]
Equity (Loss) in Undistributed Earnings in Farmers & Merchants Bank of Central California									40,597	44,571	(26,488)
Dividends from Subsidiary									19,874	13,166	73,010
Interest Income									11	17	16
Other Expenses, Net									(2,477)	(2,416)	(1,527)
Tax Benefit									729	698	516
Net Income									$ 58,734	$ 56,036	$ 45,527