Summary of Significant Accounting Policies - Self-insurance Liabilities (Details) - USD ($) $ in Millions	Dec. 25, 2024	Dec. 27, 2023
Accounting Policies [Abstract]
Workers' compensation, general, product and automobile insurance liabilities	$ 9.3	$ 9.7

Workers' Compensation, General, Product And Automobile Insurance Liability

No definition available.

Name:	denn_WorkersCompensationGeneralProductAndAutomobileInsuranceLiability
Namespace Prefix:	denn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant