ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recently adopted accounting pronouncements (Details) - USD ($) $ in Thousands		Jun. 30, 2023	Mar. 31, 2023	Jan. 01, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity		$ 242,242	$ 239,822		$ 240,864	$ 228,024	$ 223,266	$ 219,041
Allowance for credit losses: loans		22,044	19,843	$ 20,653	17,183	14,357	13,885	13,732
Allowance for credit losses on off-balance sheet exposures				3,900
Allowance for credit losses: held-to-maturity securities				71
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity		$ 51,143	$ 49,637		51,887	$ 40,195	$ 35,713	$ 30,189
Cumulative change in accounting principle
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity	[1]				(5,319)
Cumulative change in accounting principle | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity					3,470
Cumulative change in accounting principle | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity	[1]				$ (5,319)
Cumulative change in accounting principle | Retained Earnings | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total FMC stockholders’ equity				5,300
Allowance for credit losses: loans				3,500
Allowance for credit losses on off-balance sheet exposures				3,500
Allowance for credit losses: held-to-maturity securities				$ 100

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