Parent Company Financial Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Balance Sheets [Abstract]
Investment Securities	$ 473,144	$ 486,383
Other Assets	90,294	73,038
Total Assets	2,076,073	1,974,686
Subordinated Debentures	10,310	10,310
Liabilities	1,866,169	1,769,653
Shareholders' Equity	209,904	205,033	189,346	173,241
Total Liabilities and Shareholders' Equity	2,076,073	1,974,686
Condensed Statements of Income [Abstract]
Interest Income	73,640	73,351	74,380
Tax Benefit	(14,221)	(13,985)	(12,642)
Net Income	24,061	23,349	22,209
Cash Flows from Operating Activities [Abstract]
Net Income	24,061	23,349	22,209
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities: [Abstract]
Net (Increase) Decrease in Other Assets	3,719	434	2,750
Net Cash Provided by Operating Activities	27,199	31,723	30,360
Investing Activities [Abstract]
Securities Purchased	(221,745)	(143,295)	(296,852)
Securities Sold or Matured	208,962	205,374	249,930
Net Cash Used by Investing Activities	(148,890)	(29,262)	(39,835)
Financing Activities [Abstract]
Stock Repurchases	0	(576)	0
Cash Dividends	(9,723)	(9,418)	(9,158)
Net Cash Provided by Financing Activities	75,942	25,305	50,475
(Decrease) Increase in Cash and Cash Equivalents	(45,749)	27,766	41,000
Parent Company [Member]
Condensed Balance Sheets [Abstract]
Cash	416	212	398
Investment in Farmers & Merchants Bank of Central California	219,640	214,755
Investment Securities	410	410
Other Assets	87	267
Total Assets	220,553	215,644
Subordinated Debentures	10,310	10,310
Liabilities	339	301
Shareholders' Equity	209,904	205,033
Total Liabilities and Shareholders' Equity	220,553	215,644
Condensed Statements of Income [Abstract]
Equity in Undistributed Earnings in Farmers & Merchants Bank of Central California	14,352	13,247	12,715
Dividends from Subsidiary	10,450	10,900	10,325
Interest Income	10	10	10
Other Expenses, Net	(1,288)	(1,386)	(1,443)
Tax Benefit	537	578	602
Net Income	24,061	23,349	22,209
Cash Flows from Operating Activities [Abstract]
Net Income	24,061	23,349	22,209
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities: [Abstract]
Equity in Undistributed Net Earnings from Subsidiary	(14,352)	(13,247)	(12,715)
Net (Increase) Decrease in Other Assets	38	(216)	(3)
Net (Decrease) Increase in Liabilities	180	(78)	56
Net Cash Provided by Operating Activities	9,927	9,808	9,547
Investing Activities [Abstract]
Securities Purchased	0	0	(1,296)
Securities Sold or Matured	0	0	1,196
Net Cash Used by Investing Activities	0	0	(100)
Financing Activities [Abstract]
Stock Repurchases	0	(576)	0
Cash Dividends	(9,723)	(9,418)	(9,158)
Net Cash Provided by Financing Activities	(9,723)	(9,994)	(9,158)
(Decrease) Increase in Cash and Cash Equivalents	204	(186)	289
Cash and Cash Equivalents at Beginning of Year	212	398	109
Cash and Cash Equivalents at End of Year	$ 416	$ 212	$ 398