Condensed Financial Statements of Parent Company - Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash Flows from Operating Activities
Net income	$ 22,787	$ 32,515	$ 23,495
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of premiums on available-for-sale securities, net	1,500	2,090	2,203
Amortization of subordinated notes issuance fees	116	115	50
Stock-based compensation expense	1,281	899	822
Director stock awards	180	120	73
Gain on sale of available-for-sale securities	891		(293)
Changes in assets and liabilities:
Other assets and liabilities	(6,588)	(4,728)	4,586
Net cash provided by operating activities	22,146	40,669	34,741
Activity in available-for-sale securities:
Maturities, prepayments and calls	24,021	31,064	56,310
Sales	21,963		9,292
Purchases	(4,392)	(38,377)	(170,629)
Activity in certificates of deposit
Net cash used in investing activities	(194,088)	(389,904)	(265,694)
Cash Flows from Financing Activities
Proceeds (repayments) of other borrowings	(10,000)	(30,000)	40,000
Purchase of treasury stock	(218)	(308)	(338)
Proceeds from issuance of subordinated notes			34,421
Payment of dividends	(11,335)	(10,276)	(7,670)
Net cash provided by financing activities	229,734	252,821	236,070
Net Increase (Decrease) in Cash and Cash Equivalents	57,792	(96,414)	5,117
Cash and Cash Equivalents - Beginning of Year	84,409	180,823	175,706
Cash and Cash Equivalents - End of Year	142,201	84,409	180,823
Farmers & Merchants State Bank [Member]
Cash Flows from Operating Activities
Net income	22,787	32,515	23,495
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed (distributions in excess of) net income	(16,022)	9,849	(1,480)
Amortization of premiums on available-for-sale securities, net	29	61	81
Amortization of subordinated notes issuance fees	116	116	49
Stock-based compensation expense	1,281	899	822
Director stock awards	180	120	73
Gain on sale of available-for-sale securities			(293)
Changes in assets and liabilities:
Other assets and liabilities	(1,981)	2,560	(456)
Net cash provided by operating activities	6,390	46,120	22,291
Activity in available-for-sale securities:
Maturities, prepayments and calls	1,445	1,540	795
Sales	1,105		7,773
Purchases		(398)
Activity in certificates of deposit
Maturities		1,234	493
Purchases	(498)	(498)
Acquisition, net of cash received		(9,806)	(79,235)
Net cash used in investing activities	2,052	(7,928)	(70,174)
Cash Flows from Financing Activities
Proceeds (repayments) of other borrowings	(10,000)	(30,000)	35,000
Purchase of treasury stock	(218)	(308)	(338)
Proceeds from issuance of subordinated notes			34,421
Payment of dividends	(11,335)	(10,276)	(7,670)
Net cash provided by financing activities	(21,553)	(40,584)	61,413
Net Increase (Decrease) in Cash and Cash Equivalents	(13,111)	(2,392)	13,530
Cash and Cash Equivalents - Beginning of Year	16,901	19,293	5,763
Cash and Cash Equivalents - End of Year	$ 3,790	$ 16,901	$ 19,293