Commitments, Guarantees and Contingent Liabilities - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Commitments, Guarantees and Contingent Liabilities
Commitments and Loans, Available to Sell	$ 39.1	$ 8.6

Represents commitments and loans available to sell at the reporting period.

No definition available.

Name:	fdef_CommitmentsAndLoansAvailableToSell
Namespace Prefix:	fdef_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant