Parent Company Financial Information, Condensed Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Statements of Income [Abstract]
Interest Income	$ 34,188	$ 31,908	$ 30,501	$ 28,906	$ 28,076	$ 27,850	$ 26,531	$ 25,866	$ 125,503	$ 108,323	$ 95,070
Tax Benefit	(4,258)	(2,995)	(3,589)	(3,361)	(11,974)	(5,000)	(4,708)	(4,429)	(14,203)	(26,111)	(16,097)
Net Income	$ 13,036	$ 12,000	$ 10,550	$ 9,941	$ 3,781	$ 8,581	$ 8,187	$ 7,821	45,527	28,370	29,723
Parent Company [Member]
Condensed Statements of Income [Abstract]
Equity in Undistributed Earnings in Farmers & Merchants Bank of Central California									(26,488)	5,575	17,043
Dividends from Subsidiary									73,010	23,575	14,275
Interest Income									16	13	11
Other Expenses, Net									(1,527)	(1,552)	(2,485)
Tax Benefit									516	759	879
Net Income									$ 45,527	$ 28,370	$ 29,723