Income Taxes - Reconciliation of the federal statutory tax rate (Details)	12 Months Ended
Dec. 31, 2020	Dec. 26, 2019	Dec. 27, 2018	Dec. 28, 2017
Effective Income Tax Rate Reconciliation, Percent
Statutory federal tax rate	21.00%	21.00%	21.00%	35.00%
Tax benefit from Tax Cuts and Jobs Act of 2017	0.00%	0.00%	(2.90%)
Tax benefit from CARES Act and accounting method changes	10.30%
State income taxes, net of federal income tax benefit	5.00%	5.50%	6.10%
Tax credits, net of federal income tax benefit	0.20%	(2.70%)	(1.10%)
Other	(0.30%)	(1.10%)	(3.40%)
Reconciliation, Total	36.20%	22.70%	19.70%

Effective income tax rate reconciliation change in tax from CARES Act and accounting method changes.

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- Definition

Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to unrecognized tax benefits and related interest.

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- Definition

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the income tax rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Percentage of the difference, between reported income tax expense (benefit) and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, that is attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority interest income (expense), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, change in enacted tax rate, prior year income taxes, change in deferred tax asset valuation allowance, and other adjustments.

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