Basis of Accounting and Consolidation Basis of Accounting and Consolidation (ATM) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Aug. 16, 2017
At The Market Program [Member]
Balance of Common Stock Available Under ATM	$ 16,530	$ 20,000

Value of common stock available under At-The-Market Program

No definition available.

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Namespace Prefix:	fmbh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant