Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Data Type:	xbrli:sharesItemType
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Period Type:	duration

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Earnings per Share and Stock Repurchase Program (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018	Feb. 06, 2019	Jul. 27, 2015
Net (loss) income
Net income	$ 36.4	$ 36.0	$ 67.4	$ 64.2
Shares
Shares (in shares)	34,100,000	34,400,000	34,100,000	34,400,000
Per Share Amount
Net income (in dollars per share)	$ 1.06	$ 1.05	$ 1.97	$ 1.87
Dilutive securities, principally common stock options
Common stock equivalents (in shares)	100,000		100,000
Net (loss) income
Net income	$ 36.4	$ 36.0	$ 67.4	$ 64.2
Weighted average number of shares:
Shares (in shares)	34,200,000	34,400,000	34,200,000	34,400,000
Securities not included in the computation of diluted EPS
Net income (in dollars per share)	$ 1.06	$ 1.05	$ 1.97	$ 1.87
Dilutive securities, principally common stock options
Options to purchase shares of Class A common stock, anti-dilutive			0	0
Shares repurchased
Number of shares repurchased	55,988	58,579	130,397	138,634
Cost of shares repurchased	$ 4.7	$ 4.5	$ 10.3	$ 10.8
Class A
Shares repurchased
Value of shares of the entity's Class A common stock authorized to be repurchased					$ 150.0	$ 100.0
July 27, 2015 \| Class A
Shares repurchased
Remaining authorized repurchase amount	$ 1.5		$ 1.5