Commitments and Contingencies Loss Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2018
Loss Contingencies [Line Items]
Legal proceedings recorded as a liability under other noncurrent liabilities	$ (7.6)	$ (7.9)
Strack royalty payment litigation [Member]
Loss Contingencies [Line Items]
Damages sought in litigation matter	200.0
Estimated Litigation Liability, Current	$ 59.6	$ 60.6