Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Footnotes (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation	$ 1.2
NSM Holding Co LLC | Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation	0.3	$ (0.7)
NSM Holding Co LLC | Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation	1.0	(2.2)
Buzzmove | Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation	$ 0.2	$ (0.3)