Acquisition (Narrative) (Details)		12 Months Ended
	Jul. 01, 2021 USD ($) item $ / shares shares	Dec. 31, 2021 USD ($) loan	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2021 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 19,628,000	$ 7,053,000
Merger-related expenses		$ 3,033,000	2,452,000	$ 440,000
MNB Corporation [Member]
Business Acquisition [Line Items]
Merger-related expenses			$ 2,500,000
Landmark Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Number of banks held | item	1
Fair value of assets acquired including goodwill	$ 375,500,000
Loans	298,900,000				$ 298,860,000
Deposits	308,500,000
Goodwill	$ 12,575,000
Exchange ratio | shares	0.272
Shares issued | shares	647,990
Purchase price assigned to Landmark common shares exchanged for FDBC common shares	$ 35,056,259
FDBC's share price for purposes of calculation | $ / shares	$ 54.10
Cash consideration (per share) | $ / shares	$ 3.26
Number of separate fair valuation methodology employed | loan		3
Loans receivable with gross amortized cost basis	$ 309,800,000
Interest rate fair value adjustment on pools of homogeneous loans	(1,900,000)				(1,855,000)
Credit fair value discount	$ 7,900,000				$ 7,915,000
Number of branches where leases were assumed | item	2
Cash portion of purchase price	$ 7,767,586
Number of sold participations acquired | item	19
Merger-related expenses		$ 3,000,000.0
Core deposit intangibles, useful life		10 years