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Share-Based Compensation - (Narrative) (Details) $ / shares in Units, shares in Thousands, $ in Millions		12 Months Ended
	Sep. 30, 2020	Dec. 30, 2020 USD ($) plan installment $ / shares shares	Dec. 25, 2019 USD ($) $ / shares shares	Dec. 26, 2018 USD ($) $ / shares	Sep. 23, 2020 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans | plan		4
Shares available for grant (in shares) | shares		700
Income tax benefits recognized related to share-based compensation | $		$ 2.0	$ 1.7	$ 1.6
Restricted stock units for board members
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity awards granted (in shares) | shares		100
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 10.43
Vesting period		1 year
Number of equal annual installments | installment		3
Unrecognized compensation cost related to unvested awards outstanding | $		$ 0.3
Unrecognized compensation cost, expected weighted average period		4 months 24 days
Stock units converted into common stock (in shares) | shares		100
Stock units outstanding (in shares) | shares		800	700
Employee share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 10.47	$ 19.02	$ 16.97
Cash payments | $		$ 0.2	$ 0.4	$ 0.2
Intrinsic value of units converted | $		12.0	16.9	$ 9.8
Accrued compensation included as a component of other current liabilities | $		0.1	0.1
Accrued compensation included as a component of other noncurrent liabilities | $		0.2	$ 0.2
Unrecognized compensation cost related to unvested awards outstanding | $		$ 8.8
Unrecognized compensation cost, expected weighted average period		1 year 3 months 18 days
Stock units outstanding (in shares) | shares		1,563	1,681
2020 Employee Share Awards | Restricted stock units for board members
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity awards granted (in shares) | shares		800
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 10.47
Vesting period		2 years
2017 Omnibus Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares) | shares		2,000
2018 | Employee share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Percentage of awards issued	100.00%
Percentage of growth in earnings	50.00%
Percentage of relative total stockholder return	50.00%
Award initial measurement period		2 years
Number of shares affected (in shares) | shares		200
Fair value of shares affected | $		$ 2.4			$ 0.0
Fair value of shares affected (in dollars per share) | $ / shares		$ 10.00
Percentage of target		100.00%
Total percentage of target		150.00%
2019 | Employee share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 8.24
Vesting period	3 years
Percentage of awards issued	100.00%
Percentage of growth in earnings	50.00%
Percentage of relative total stockholder return	50.00%
Number of shares affected (in shares) | shares		300
Fair value of shares affected | $		$ 2.3			$ 0.0
Remaining term		15 months

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Aggregate carrying value as of the balance sheet date of the liabilities for stock option plans and other equity-based compensation arrangements payable within one year (or the operating cycle, if longer).

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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