Income Taxes - Effective Income Tax Rate Reconciliation, Amount (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2015
Income Tax Disclosure [Abstract]
Statutory U.S. federal income tax - provision (benefit)	$ 3.1	$ 30.4	$ 10.2	$ (5.6)
State income taxes	0.4	7.0	3.2	5.9
Reserve adjustments	0.0	(4.6)	(0.3)	0.4
Non-deductible convertible subordinated notes interest	0.1	0.0	0.8	1.4
R&D credits	(0.2)	(1.2)	(4.1)	0.0
Retroactive change in federal tax law	(1.7)	0.0	0.0	(1.9)
Benefit of manufacturing deductions	(0.6)	0.0	0.5	(1.0)
Lobbying costs	0.0	0.7	0.8	0.6
Deferred tax adjustment	0.7	(0.1)	(0.4)	0.0
Stock compensation excess tax benefits	0.0	(1.4)	0.0	0.0
Other, net	0.2	0.7	0.5	0.5
New legislation - tax rate changes	0.0	64.6	0.0	0.0
Income tax provision	$ 2.0	$ 96.1	$ 11.2	$ 0.3