Intangible Assets - Schedule of Finite-lived Intangible Assets (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Cost
Intangible assets, gross	$ 828.4	$ 818.4	$ 151.4
Finite-lived intangible assets acquired	10.0	667.0
Finite-lived intangible assets, accumulated amortization	(100.7)	(56.8)
Intangible assets, net	727.7	761.6
Goodwill [Roll Forward]
Goodwill, cost	268.6	259.7	$ 49.1
Goodwill, measurement period adjustments	8.9
Goodwill, acquired during period		210.6
Goodwill	$ 268.6	$ 259.7
Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization period of intangible asset	5 years	5 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization period of intangible asset	22 years	22 years
IPR&D
Indefinite-lived Intangible Assets [Roll Forward]
Indefinite-lived intangible assets (excluding goodwill)	$ 50.0	$ 50.0
Indefinite-lived intangible assets, purchase accounting adjustments	(9.0)
Indefinite-lived intangible assets (excluding goodwill)	$ 41.0	$ 50.0