ESOP (Details) - USD ($)		12 Months Ended
Jul. 31, 2024	Dec. 31, 2024
ESOP
Employee Stock Ownership Plan (ESOP), Loan Amount	$ 4,447,580
Employee Stock Ownership Plan (ESOP), Shares Contributed to ESOP	444,758
ESOP term	20 years
ESOP loan interest rate (as a percent)	8.50%
ESOP loan quarterly principal and interest payments	$ 112,000
ESOP Contribution		$ 449,000
ESOP Compensation Expense		246,000
Fair value of unallocated ESOP shares		$ 4,497,000

The amount of loan given by the entity to the Employee Stock Ownership Plan ESOP.

No definition available.

Name:	fdsb_EmployeeStockOwnershipPlanEsopLoanAmount
Namespace Prefix:	fdsb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The interest rate on the loan given by the entity to the Employee Stock Ownership Plan ESOP.

+ References

No definition available.

+ Details

Name:	fdsb_EmployeeStockOwnershipPlanEsopLoanInterestRate
Namespace Prefix:	fdsb_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The quarterly principal and interest payments on loan given by the entity to the Employee Stock Ownership Plan ESOP.

+ References

No definition available.

+ Details

Name:	fdsb_EmployeeStockOwnershipPlanEsopQuarterlyLoanPrincipalAndInterestPayments
Namespace Prefix:	fdsb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Period of time between issuance and maturity of financing receivable, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	fdsb_FinancingReceivableTerm
Namespace Prefix:	fdsb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_DisclosureOfCompensationRelatedCostsSharebasedPaymentsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This item represents the amount of cash contributions during the period made by the entity to the Employee Stock Ownership Plan (ESOP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480489/718-40-50-1

+ Details

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

- Definition

The amount of plan compensation cost recognized during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480489/718-40-50-1

+ Details

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

- Definition

Fair value of unearned shares held by the employee stock ownership plan (ESOP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480489/718-40-50-1

+ Details

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

- Definition

This item represents the number of shares provided to the Employee Stock Ownership Plan (ESOP) during the period.

+ References

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPSharesContributedToESOP
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration