(Loss) Income Per Share (In millions of dollars, except shares and per share data) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net (loss) income									$ (6.6)	$ 9.4	$ 38.3
Denominator:
Average common shares outstanding (in shares)									89,022,531	88,590,491	88,323,213
Other potentially dilutive common shares (in shares)									0	856,426	564,599
Average common shares outstanding, assuming dilution (in shares)									89,022,531	89,446,917	88,887,812
Net (loss) income per share, basic (in dollars per share)	$ (0.04)	$ 0.04	$ (0.01)	$ (0.07)	$ 0.03	$ (0.06)	$ 0.11	$ 0.02	$ (0.07)	$ 0.11	$ 0.43
Net (loss) income per share, assuming dilution (in dollars per share)	$ (0.04)	$ 0.04	$ (0.01)	$ (0.07)	$ 0.03	$ (0.06)	$ 0.11	$ 0.02	$ (0.07)	$ 0.11	$ 0.43
Stock Option
Denominator:
Antidilutive stock awards excluded from calculation (in shares)									5,100,000	1,400,000	1,700,000