Acquisitions - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions				3 Months Ended	9 Months Ended
	Aug. 19, 2019	Jul. 31, 2019	Jul. 18, 2019	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Aratana
Business Acquisition [Line Items]
Number of shares issued to previous shareholders upon closing (in shares)			7.2
Value of shares issued as consideration			$ 238.0
Maximum aggregate contingent payment			$ 12.0
Business acquisition (usd per share)			$ 0.25
Average useful life			12 years 6 months
Accelerated vesting of equity awards (in shares)				0.1
Accelerated stock based compensation expense				$ 3.6
Revenues				3.8
Pro forma combined revenues					$ 2,300.0	$ 2,300.0
Pro forma combined income before income taxes					66.9	$ 98.9
Prevtec
Business Acquisition [Line Items]
Maximum aggregate contingent payment		$ 16.3		16.3	16.3
Contingent consideration liability		$ 4.7
Average useful life		10 years
Consideration transferred		$ 60.3
Bayer Animal Business
Business Acquisition [Line Items]
Value of shares issued as consideration	$ 2,300.0
Amount paid at closing	$ 5,300.0
Galliprant
Business Acquisition [Line Items]
Contingent consideration liability			$ 84.7
Loss upon settlement of contingent consideration liability				$ 7.5	$ 7.5