Parent Company Financial Information, Condensed Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Statements of Income [Abstract]
Interest Income	$ 35,654	$ 35,280	$ 35,373	$ 34,207	$ 34,188	$ 31,908	$ 30,501	$ 28,906	$ 140,514	$ 125,503	$ 108,323
Tax Benefit	(5,037)	(4,660)	(4,903)	(4,677)	(4,258)	(2,995)	(3,589)	(3,361)	(19,277)	(14,203)	(26,111)
Net Income	$ 14,644	$ 13,738	$ 14,105	$ 13,549	$ 13,036	$ 12,000	$ 10,550	$ 9,941	56,036	45,527	28,370
Parent Company [Member]
Condensed Statements of Income [Abstract]
Equity (Loss) in Undistributed Earnings in Farmers & Merchants Bank of Central California									44,571	(26,488)	5,575
Dividends from Subsidiary									13,166	73,010	23,575
Interest Income									17	16	13
Other Expenses, Net									(2,416)	(1,527)	(1,552)
Tax Benefit									698	516	759
Net Income									$ 56,036	$ 45,527	$ 28,370