Shareholders' Equity - Changes in Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Increase (Decrease) in Stockholders' Equity
Other comprehensive income (loss)	$ 23.3		$ (2.6)		$ 1.7	$ 4.2
Cash dividends per share, declared (in dollars per share)	$ 0.26	$ 0.26	$ 0.25	$ 0.25
Total Permanent Shareholders' Equity
Increase (Decrease) in Stockholders' Equity
Beginning balance	$ 1,071.9	$ 886.9	$ 871.1	$ 857.7	886.9	857.7
Net income (loss)	(6.5)	218.7	23.9	13.1
Other comprehensive income (loss)	22.7	(22.5)	(2.6)	6.8
Dividends ($0.26 per share)	(5.4)	(5.3)	(5.2)	(5.3)
Share repurchases		(5.3)	(12.6)	(2.4)
Incentive plan activity	1.5	1.0	1.6	1.2
Other		(1.5)
Ending balance	1,084.2	1,071.9	876.2	871.1	1,084.2	876.2
Total Permanent Shareholders' Equity | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity
Beginning balance		(0.1)			(0.1)
Common Stock
Increase (Decrease) in Stockholders' Equity
Beginning balance	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2
Balance (in shares)	20.5	20.6	20.8	20.7	20.6	20.7
Shares repurchases (in shares)		(0.1)	(0.2)		(0.1)
Incentive plan activity (in shares)				0.1
Ending balance	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2
Balance (in shares)	20.5	20.5	20.6	20.8	20.5	20.6
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity
Beginning balance	$ 286.3	$ 292.1	$ 299.8	$ 301.0	$ 292.1	$ 301.0
Share repurchases		(5.3)	(12.6)	(2.4)
Incentive plan activity	1.5	1.0	1.6	1.2
Other		(1.5)
Ending balance	287.8	286.3	288.8	299.8	287.8	288.8
Retained Earnings
Increase (Decrease) in Stockholders' Equity
Beginning balance	845.5	632.2	622.6	603.3	632.2	603.3
Net income (loss)	(6.5)	218.7	23.9	13.1
Dividends ($0.26 per share)	(5.4)	(5.3)	(5.2)	(5.3)
Ending balance	833.6	845.5	641.3	622.6	833.6	641.3
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity
Beginning balance		(0.1)		11.5	(0.1)	11.5
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity
Beginning balance	(58.9)	(36.4)	(50.2)	(45.5)	(36.4)	(45.5)
Other comprehensive income (loss)	22.7	(22.5)	(2.6)	6.8
Ending balance	(36.2)	(58.9)	(52.8)	(50.2)	(36.2)	(52.8)
Accumulated Other Comprehensive Loss | Cumulative Effect, Period of Adoption, Adjustment
Increase (Decrease) in Stockholders' Equity
Beginning balance				(11.5)		(11.5)
Treasury Stock
Increase (Decrease) in Stockholders' Equity
Beginning balance	(1.2)	(1.2)	(1.3)	(1.3)	(1.2)	(1.3)
Ending balance	(1.2)	(1.2)	$ (1.3)	$ (1.3)	(1.2)	$ (1.3)
Redeemable Non-controlling Interest
Increase (Decrease) in Stockholders' Equity
Beginning balance	29.0	28.0			28.0
Net income (loss)	0.1	0.1
Other comprehensive income (loss)	0.6	0.9
Ending balance	$ 29.7	$ 29.0			$ 29.7