Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock Capital Stock, Class A common stock	Common Stock Capital Stock, Class B common stock	Treasury Stock Treasury Stock, Class A common stock	Treasury Stock Treasury Stock, Class B common stock	Paid-in Capital	Earnings Invested in the Business	Accumulated Other Comprehensive Income (Loss)	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjustment Earnings Invested in the Business
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 30, 2018		$ 36.6	$ 3.5	$ (25.4)	$ (0.6)	$ 24.4	$ 1,138.1	$ (17.1)
Increase (Decrease) in Stockholders' Equity
Net issuance of stock awards				4.5	0.0	(1.2)
Net earnings (loss)	$ 105.9						105.9
Dividends							(5.9)
Other comprehensive income (loss), net of tax	5.4							5.4
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2019	$ 1,268.2	36.6	3.5	(20.9)	(0.6)	23.2	1,238.1	(11.7)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 30, 2018		36.6	3.5	(25.4)	(0.6)	24.4	1,138.1	(17.1)
Stockholders' Equity Attributable to Parent, Ending Balance at Dec. 29, 2019	$ 1,264.5	36.6	3.5	(20.3)	(0.6)	22.5	1,238.6	(15.8)		$ (0.7)
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 31, 2019		36.6	3.5	(21.3)	(0.6)	21.0	1,157.2	(18.6)
Increase (Decrease) in Stockholders' Equity
Net issuance of stock awards				0.4	0.0	2.2
Net earnings (loss)	83.8						83.8
Dividends							(2.9)
Other comprehensive income (loss), net of tax	6.9							6.9
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 30, 2019	1,268.2	36.6	3.5	(20.9)	(0.6)	23.2	1,238.1	(11.7)
Increase (Decrease) in Stockholders' Equity
Earnings invested in the business	1,238.6
Stockholders' Equity Attributable to Parent, Beginning Balance at Dec. 29, 2019	1,264.5	36.6	3.5	(20.3)	(0.6)	22.5	1,238.6	(15.8)		$ (0.7)
Increase (Decrease) in Stockholders' Equity
Net issuance of stock awards				3.6	0.0	(2.0)
Net earnings (loss)	(112.1)						(112.1)
Dividends							(3.0)
Other comprehensive income (loss), net of tax	(4.7)							(4.7)
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 28, 2020	1,145.6	36.6	3.5	(16.7)	(0.6)	20.5	1,122.8	(20.5)
Increase (Decrease) in Stockholders' Equity
Earnings invested in the business | Accounting Standards Update 2016-13									$ (0.7)
Stockholders' Equity Attributable to Parent, Beginning Balance at Mar. 29, 2020		36.6	3.5	(17.4)	(0.6)	19.5	1,081.7	(23.2)
Increase (Decrease) in Stockholders' Equity
Net issuance of stock awards				0.7	0.0	1.0
Net earnings (loss)	41.1						41.1
Dividends							0.0
Other comprehensive income (loss), net of tax	2.7							2.7
Stockholders' Equity Attributable to Parent, Ending Balance at Jun. 28, 2020	1,145.6	$ 36.6	$ 3.5	$ (16.7)	$ (0.6)	$ 20.5	$ 1,122.8	$ (20.5)
Increase (Decrease) in Stockholders' Equity
Earnings invested in the business	$ 1,122.8