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

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- Definition Workers' Compensation, General, Product And Automobile Insurance Liability + References No definition available. + Details
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Namespace Prefix: | denn_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration