Non-Qualified Retirement, Savings and Investment Plans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) plan shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)
Retirement Benefits [Abstract]
Number of non-qualified retirement savings and investment plans | plan	2
Deferred compensation liability, current and long-term	$ 26.1	$ 27.3
Number of Deferred Compensation Plans | plan	2
Increase (decrease) in compensation expense	$ (0.7)	3.7	$ 2.1
Deferred compensation plan assets	21.3	22.6
Restricted investments, current	1.9
Investment gains (losses)	$ (1.3)	$ 3.2	$ 1.5
Deferred compensation arrangement with individual, shares issued (in shares) | shares	0	0