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Purchase price of common stock expressed as a percentage of its fair value.

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Stock-Based Compensation (Details) - $ / shares	3 Months Ended	9 Months Ended		12 Months Ended
Stock-Based Compensation (Details) - $ / shares	Sep. 27, 2020	Sep. 26, 2021	Sep. 27, 2020	Dec. 31, 2020
Second Amended and Restated 2004 Stock Incentive Plan
Stock-based compensation
Vesting period		3 years
Second Amended and Restated 2004 Stock Incentive Plan \| Restricted Stock and Deferred Shares
Stock-based compensation
Granted (in shares)		59,957	85,488
Second Amended and Restated 2004 Stock Incentive Plan \| Performance stock units
Stock-based compensation
Vesting period		3 years
Granted (in shares)	73,106	46,774
Management Stock Purchase Plan \| Maximum
Stock-based compensation
Percentage of annual incentive bonus that may be used to purchase RSU's		50.00%
Management Stock Purchase Plan \| Class A
Stock-based compensation
Purchase price as percentage of fair market value of common stock on grant date		80.00%
Management Stock Purchase Plan \| Restricted stock units (RSUs)
Stock-based compensation
Granted (in shares)		24,690	27,495
Fair value assumptions
Expected life (years)		3 years		3 years
Expected stock price volatility (as a percent)		32.70%		24.60%
Expected dividend yield (as a percent)		0.75%		1.10%
Risk-free interest rate (as a percent)		0.30%		0.60%
Weighted average grant-date fair value (in dollars per share)		$ 37.12	$ 22.36