Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income	$ 17.8	$ 47.9	$ 39.3	$ 46.3	$ 56.6	$ 45.1	$ 68.0	$ 41.5	$ 151.3	$ 211.2	$ 211.3
Denominator:
Denominator for basic earnings per share — weighted average shares									35.0	35.7	37.6
Effect of dilutive securities:
Equity compensation plans									0.4	0.7	0.7
Denominator for diluted earnings per share — adjusted weighted average and assumed conversion									35.4	36.4	38.3
Basic earnings per share (in dollars per share)	$ 0.51	$ 1.37	$ 1.12	$ 1.33	$ 1.62	$ 1.28	$ 1.89	$ 1.14	$ 4.33	$ 5.92	$ 5.62
Diluted earnings per share (in dollars per share)	0.50	1.35	1.11	1.31	$ 1.59	$ 1.25	$ 1.86	$ 1.12	$ 4.27	$ 5.81	$ 5.52
Income from continuing operations					$ 42.1	$ 37.2	$ 60.3	$ 41.2	$ 150.2	$ 180.8	$ 190.5
Income (Loss) from Continuing Operations, Per Basic Share	0.51	1.38	1.06	1.35	$ 1.21	$ 1.05	$ 1.68	$ 1.13	$ 4.30	$ 5.07	$ 5.07
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Basic Share	$ 0	$ (0.01)	$ 0.06	$ (0.02)	$ 0.41	$ 0.23	$ 0.21	$ 0.01	$ 0.03	$ 0.85	$ 0.55
Total Discontinued Operations, Net of Taxes	$ 0.0	$ (0.3)	$ 2.3	$ (0.9)	$ 14.5	$ 7.9	$ 7.7	$ 0.3	$ 1.1	$ 30.4	$ 20.8
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.50	$ 1.36	$ 1.05	$ 1.33	$ 1.18	$ 1.03	$ 1.65	$ 1.11	$ 4.24	$ 4.97	$ 4.98
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Per Diluted Share	$ 0	$ (0.01)	$ 0.06	$ (0.02)	$ 0.41	$ 0.22	$ 0.21	$ 0.01	$ 0.03	$ 0.84	$ 0.54