Goodwill and Other Long-Lived Assets - Changes in Carrying Amount of Goodwill (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 2,294,479
Accumulated impairment losses, beginning balance	(130,057)
Subtotal, beginning balance	2,164,422
Goodwill acquired	75,884
Foreign translation adjustment	1,738
Other	(13,855)
Goodwill, ending balance	2,358,246
Accumulated impairment losses, ending balance	(130,057)
Subtotal, ending balance	2,228,189
Animal Hospital
Goodwill [Roll Forward]
Goodwill, beginning balance	2,047,894
Accumulated impairment losses, beginning balance	0
Subtotal, beginning balance	2,047,894
Goodwill acquired	75,884
Foreign translation adjustment	1,733
Other	(13,855)
Goodwill, ending balance	2,111,656
Accumulated impairment losses, ending balance	0
Subtotal, ending balance	2,111,656
Laboratory
Goodwill [Roll Forward]
Goodwill, beginning balance	101,283
Accumulated impairment losses, beginning balance	0
Subtotal, beginning balance	101,283
Goodwill acquired	0
Foreign translation adjustment	5
Other	0
Goodwill, ending balance	101,288
Accumulated impairment losses, ending balance	0
Subtotal, ending balance	101,288
All Other
Goodwill [Roll Forward]
Goodwill, beginning balance	145,302
Accumulated impairment losses, beginning balance	(130,057)
Subtotal, beginning balance	15,245
Goodwill acquired	0
Foreign translation adjustment	0
Other	0
Goodwill, ending balance	145,302
Accumulated impairment losses, ending balance	(130,057)
Subtotal, ending balance	$ 15,245