Acquisitions - Acquisition and Disposal Activity (Details)	3 Months Ended
	Mar. 31, 2017 Laboratory Hospital	Mar. 31, 2016 Laboratory Hospital
Laboratories Acquisitions
Business Acquisition Summary Of Acquired Properties [Line Items]
Net increase | Laboratory	0	0
Animal Hospital
Business Acquisition Summary Of Acquired Properties [Line Items]
Acquisitions	15	24
Acquisitions, merged	0	(1)
Sold, closed or merged	0	(2)
Net increase	15	21