Note 8 - Fair Value Measurements (Details Textual) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	$ 0	$ 0
Other Repossessed Assets	$ 0	$ 0
Measurement Input, Cost to Sell [Member] \| Minimum [Member]
Impaired Loans, Measurement Input	(0.2596)	(0.1961)
Measurement Input, Cost to Sell [Member] \| Maximum [Member]
Impaired Loans, Measurement Input	(0.3019)	(0.2958)
Measurement Input, Cost to Sell [Member] \| Weighted Average [Member]
Impaired Loans, Measurement Input	(0.2775)	(0.2177)
Measurement Input, Discount Rate [Member] \| Minimum [Member]
Other Real Estate Owned, Measurement Input	(0.7760)	(0.3907)
Measurement Input, Discount Rate [Member] \| Maximum [Member]
Other Real Estate Owned, Measurement Input	(0.7760)	(0.7760)
Measurement Input, Discount Rate [Member] \| Weighted Average [Member]
Other Real Estate Owned, Measurement Input	(0.7760)	(0.3961)

The measurement input for impaired loans.

No definition available.

Name:	fdbc_ImpairedLoansMeasurementInput
Namespace Prefix:	fdbc_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of assets other than real property that were received in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-3

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11

+ Details

Name:	us-gaap_OtherForeclosedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Value of input used to measure real estate owned by financial institution by financial institution which is not directly related to its business.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

+ Details

Name:	us-gaap_OtherRealEstateOwnedMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputCostToSellMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: