Condensed Financial Statements of Parent Company - Statements of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash Flows from Operating Activities
Net income	$ 9,646us-gaap_NetIncomeLoss	$ 9,007us-gaap_NetIncomeLoss	$ 9,788us-gaap_NetIncomeLoss
Changes in Assets and Liabilities:
Net cash provided by operating activities	19,159	16,993	14,214
Cash Flows from Investing Activities
Net cash provided by (used in) investing activities	22,507	(31,957)	(26,454)
Cash Flows from Financing Activities
Payment of dividends	(3,864)us-gaap_PaymentsOfDividendsCommonStock	(3,719)us-gaap_PaymentsOfDividendsCommonStock	(3,597)us-gaap_PaymentsOfDividendsCommonStock
Purchase of Treasury Stock	(576)	(1,236)	(894)
Net cash provided by (used in) financing activities	(36,634)	(9,865)	13,189
Net Change in Cash and Cash Equivalents	5,032	(24,829)	949
Cash and Cash Equivalents
Cash and Cash Equivalents - Beginning of Year	19,263	44,092	43,143
Cash and Cash Equivalents - End of Year	24,295	19,263	44,092
Farmers & Merchants State Bank [Member]
Cash Flows from Operating Activities
Net income	9,646	9,007	9,788
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:
Equity in undistributed net income (Distributions in excess earnings) of subsidiaries	(4,087)	(4,974)	(5,649)
Accretion & Amortization of Securities	146	21
Changes in Assets and Liabilities:
Dividends receivable	(1,025)	(10)	260
Other Assets and Liabilities	(12)	52	282
Net cash provided by operating activities	4,668	4,096	4,681
Cash Flows from Investing Activities
Investing in Subsidiary	(250)
Purchase of Available for Sale Securities		(14,992)
Repayment of Subsidiary Subordinated Debt		15,000
Net cash provided by (used in) investing activities	(250)	8
Cash Flows from Financing Activities
Payment of dividends	(3,862)	(3,719)	(3,597)
Purchase of Treasury Stock	(576)	(1,236)	(894)
Net cash provided by (used in) financing activities	(4,438)	(4,955)	(4,491)
Net Change in Cash and Cash Equivalents	(20)	(851)	190
Cash and Cash Equivalents
Cash and Cash Equivalents - Beginning of Year	322	1,173	983
Cash and Cash Equivalents - End of Year	$ 302	$ 322	$ 1,173

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