Goodwill and Other Long-Lived Assets - Changes in Carrying Amount of Goodwill (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($)
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 1,647,707
Accumulated impairment losses, beginning balance	(130,057)
Subtotal, beginning balance	1,517,650
Goodwill acquired	434,835
Foreign translation adjustment	9,066
Other	1,826
Goodwill, ending balance	2,093,434
Accumulated impairment losses, ending balance	(130,057)
Subtotal, ending balance	1,963,377
Animal Hospital
Goodwill [Roll Forward]
Goodwill, beginning balance	1,402,106
Accumulated impairment losses, beginning balance	0
Subtotal, beginning balance	1,402,106
Goodwill acquired	434,323
Foreign translation adjustment	9,034
Other	1,826
Goodwill, ending balance	1,847,289
Accumulated impairment losses, ending balance	0
Subtotal, ending balance	1,847,289
Laboratory
Goodwill [Roll Forward]
Goodwill, beginning balance	101,269
Accumulated impairment losses, beginning balance	0
Subtotal, beginning balance	101,269
Goodwill acquired	0
Foreign translation adjustment	32
Other	0
Goodwill, ending balance	101,301
Accumulated impairment losses, ending balance	0
Subtotal, ending balance	101,301
All Other
Goodwill [Roll Forward]
Goodwill, beginning balance	144,332
Accumulated impairment losses, beginning balance	(130,057)
Subtotal, beginning balance	14,275
Goodwill acquired	512
Foreign translation adjustment	0
Other	0
Goodwill, ending balance	144,844
Accumulated impairment losses, ending balance	(130,057)
Subtotal, ending balance	$ 14,787