CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Paid-In Capital	Retained Deficit	Retained Deficit Cumulative Effect, Period of Adoption, Adjustment	Accum. Other Comprehensive Income	Common Stock In Treasury
Balance at beginning of period at Dec. 31, 2018	$ 414.9		$ 0.5	$ 1,295.4	$ (650.1)		$ 244.9	$ (475.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	39.9				39.9
Other comprehensive income (loss), net	(5.0)						(5.0)
Incentive plan activity	10.0			10.0
Long-term incentive compensation expense	8.1			8.1
Restricted stock and restricted stock unit vesting	(6.6)			(22.3)				15.7
Balance at end of period at Sep. 28, 2019	461.3		0.5	1,291.2	(610.2)		239.9	(460.1)
Balance at beginning of period at Jun. 29, 2019	436.7		0.5	1,285.3	(631.7)		242.7	(460.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	21.5				21.5
Other comprehensive income (loss), net	(2.8)						(2.8)
Incentive plan activity	3.1			3.1
Long-term incentive compensation expense	2.8			2.8
Restricted stock and restricted stock unit vesting	0.0
Balance at end of period at Sep. 28, 2019	461.3		0.5	1,291.2	(610.2)		239.9	(460.1)
Balance at beginning of period at Dec. 31, 2019	502.4	$ (0.5)	0.5	1,302.4	(584.8)	$ (0.5)	244.3	(460.0)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	72.6				72.6
Other comprehensive income (loss), net	(7.1)						(7.1)
Incentive plan activity	10.7			10.7
Long-term incentive compensation expense	9.3			9.3
Restricted stock and restricted stock unit vesting	(4.3)			(12.7)				8.4
Balance at end of period at Sep. 26, 2020	$ 583.1		0.5	1,309.7	(512.7)		237.2	(451.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Balance at beginning of period at Jun. 27, 2020	$ 552.1		0.5	1,303.4	(535.5)		235.3	(451.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	22.8				22.8
Other comprehensive income (loss), net	1.9						1.9
Incentive plan activity	3.1			3.1
Long-term incentive compensation expense	3.2			3.2
Restricted stock and restricted stock unit vesting	0.0
Balance at end of period at Sep. 26, 2020	$ 583.1		$ 0.5	$ 1,309.7	$ (512.7)		$ 237.2	$ (451.6)