Revenues - Topic 606 Income Statement (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 1,114.0	$ 1,051.6	$ 1,026.0
Operating expenses	625.4	569.5	582.6
Depreciation and amortization	217.0	206.5	208.3
Income tax expense (benefit)	37.7	(61.8)	25.8
Net earnings	$ 168.5	$ 254.2	$ 133.0
Basic (in dollars per share)	$ 1.14	$ 2.06	$ 0.69
Diluted (in dollars per share)	$ 1.14	$ 1.47	$ 0.67
ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 1,102.4
Operating expenses	629.9
Depreciation and amortization	215.9
Income tax expense (benefit)	33.8
Net earnings	$ 157.4
Basic (in dollars per share)	$ 1.07
Diluted (in dollars per share)	$ 1.06
Adjustments for ASC 606 Adoption [Member] | ASU 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ (11.6)
Operating expenses	4.5
Depreciation and amortization	(1.1)
Income tax expense (benefit)	(3.9)
Net earnings	$ (11.1)
Basic (in dollars per share)	$ (0.07)
Diluted (in dollars per share)	$ (0.08)