Condensed Financial Statements of Parent Company - Statement of Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income
Interest									$ 24,978	$ 26,489	$ 29,840
Total Income	8,117	7,844	7,765	7,702	7,994	8,278	8,525	8,476	31,428	33,273	36,660
Income Before Income Taxes and Equity in Undistributed Earnings (Distributions in excess of earnings) and Subsidiary	3,151	2,857	3,511	3,084	3,532	3,388	3,558	3,214	12,603	13,692	11,407
Income Taxes	864	791	1,009	932	1,007	947	1,020	930	3,596	3,904	2,893
Net Income	2,287	2,066	2,502	2,152	2,525	2,441	2,538	2,284	9,007	9,788	8,514
Other Comprehensive Loss:
Unrealized losses on securities									(6,087)	(288)	5,843
Comprehensive Income									2,920	9,500	14,357
Farmers & Merchants State Bank [Member]
Income
Dividends from subsidiary									3,830	3,870	4,000
Interest									566	713	713
Interest Municipals									30
Total Income									4,426	4,583	4,713
Operating Expenses									304	305	499
Income Before Income Taxes and Equity in Undistributed Earnings (Distributions in excess of earnings) and Subsidiary									4,122	4,278	4,214
Income Taxes									89	139	72
Income from operation before equity in undistributed earnings of subsidiary									4,033	4,139	4,142
Equity in undistributed earnings (Distributions in excess of earnings) of subsidiary									4,974	5,649	4,372
Net Income									9,007	9,788	8,514
Other Comprehensive Loss:
Unrealized losses on securities									(15)
Comprehensive Income									$ 8,992	$ 9,788	$ 8,514