ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recently adopted accounting pronouncements (Details) - USD ($)		Mar. 31, 2023	Jan. 01, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity		$ 239,822,000		$ 240,864,000	$ 223,266,000	$ 219,041,000
Allowance for credit losses: loans		19,843,000	$ 20,653,000	17,183,000	13,885,000	13,732,000
Allowance for credit losses on off-balance sheet exposures			3,900,000
Allowance for credit losses: held-to-maturity securities			71,000
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity		$ 49,637,000		51,887,000	$ 35,713,000	$ 30,189,000
Cumulative adjustment for day one adoption of ASC 326, net of tax
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity	[1]			(5,319,000)
Cumulative adjustment for day one adoption of ASC 326, net of tax | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity				3,470,000
Cumulative adjustment for day one adoption of ASC 326, net of tax | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity	[1]			$ (5,319,000)
Cumulative adjustment for day one adoption of ASC 326, net of tax | Retained Earnings | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity			5,300,000
Allowance for credit losses: loans			3,500,000
Allowance for credit losses on off-balance sheet exposures			3,500,000
Allowance for credit losses: held-to-maturity securities			$ 100,000

[1] Refer to Note 1 - Organization and Summary of Significant Accounting Policies for further information.