Actual percentage achieved.

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Period over which plan activity is adjusted to determine the maximum number of shares that may be issued in accordance with the plan.

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Share-based Compensation Arrangement by Share-based Payment Award, Performance Measurement Period

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The weighted average fair value at grant date for nonvested equity-based awards issued 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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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of additional shares authorized for issuance under an established share-based compensation plan.

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No definition available.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

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Percentage of vesting of share-based compensation awards.

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Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 30, 2018	Dec. 31, 2017	Jan. 01, 2017	Apr. 01, 2018	Feb. 14, 2018	Feb. 15, 2017	Feb. 17, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Plan activity adjustment period - Evergreen provision	5 years
Number of shares available for grant (in shares) - Fixed provision	4,000,000
Tax benefit	$ 4.4	$ 4.2	$ 3.9
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Unrecognized compensation cost, unvested restricted stock	$ 6.1
Compensation cost not yet recognized, period for recognition	1 year 9 months 18 days
Grants in period (in dollars per share)	$ 28.79	$ 21.97	$ 17.08
Vested in period, fair value	$ 4.9	$ 5.8	$ 6.4
Granted (in shares)	157,000
Weighted average grant date fair value (in dollars per share)	$ 23.44	$ 18.76
Total nonvested shares (in shares)	356,000	440,000
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	222,000	387,000	332,000
Performance Shares, Financial Goals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, unvested restricted stock	$ 2.1
Compensation cost not yet recognized, period for recognition	1 year 8 months 12 days
Vested in period, fair value	$ 7.7
Granted (in shares)	118,000	203,000	249,000
Performance measurement period	3 years	3 years	3 years
Weighted average grant date fair value (in dollars per share)					$ 28.40	$ 21.07	$ 15.85
Performance Shares, Total Shareholder Return
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, unvested restricted stock	$ 1.6
Compensation cost not yet recognized, period for recognition	1 year 8 months 12 days
Grants in period (in dollars per share)	$ 31.38
Vested in period, fair value	$ 6.3
Granted (in shares)	59,000	101,000	83,000
Performance measurement period	3 years	3 years	3 years
Weighted average grant date fair value (in dollars per share)	$ 23.56	$ 18.17
Total nonvested shares (in shares)	173,000	240,000
Performance Shares, Total Shareholder Return \| Monte Carlo Fair Value
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)					$ 31.38	$ 20.16	$ 19.73
Performance Shares, Single Financial Goal
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years	4 years
Granted (in shares)	45,000	83,000
Performance measurement period	1 year	1 year
Stock-based compensation cost
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation cost	$ 8.1	$ 9.1	$ 10.2
Class A common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares available for grants - Evergreen provision	15.00%
Maximum number of shares available for grants - Fixed provision	4,700,000
Performance shares eligible to earn more than target \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	177,000	304,000
Maximum shares eligible to earn \| Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	355,000	609,000	663,000
Maximum target percentage allowed under grant	200.00%	200.00%	200.00%
Maximum shares eligible to earn \| Performance Shares, Financial Goals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum target percentage allowed under grant	200.00%	200.00%	200.00%
Maximum shares eligible to earn \| Performance Shares, Total Shareholder Return
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum target percentage allowed under grant	200.00%	200.00%	200.00%
2018 grant \| Performance Shares, Financial Goals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)	$ 19.41
Total nonvested shares (in shares)	219,000
2018 grant \| Performance Shares, Total Shareholder Return
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total nonvested shares (in shares)	109,000
2017 grant \| Performance Shares, Financial Goals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)	$ 19.41
Total nonvested shares (in shares)	254,000
2017 grant \| Performance Shares, Total Shareholder Return
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total nonvested shares (in shares)	127,000
2016 grant \| Performance Shares, Financial Goals
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value (in dollars per share)				$ 28.40
Total nonvested shares (in shares)	117,000
Actual percentage achieved	70.00%
2016 grant \| Performance Shares, Total Shareholder Return
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total nonvested shares (in shares)	57,000
Actual percentage achieved	104.00%