Commitments, Guarantees and Contingent Liabilities - Additional Information (Details)	3 Months Ended
Mar. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Loan Commitments Maturities Range Description	60 days or less

Description of the maturities range of loan commitments

No definition available.

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Namespace Prefix:	fdef_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration