Goodwill and Other Long-Lived Assets - Changes in Carrying Amount of Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 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	537,001
Foreign translation adjustment	6,681
Other	2,162
Goodwill, ending balance	2,193,551
Accumulated impairment losses, ending balance	(130,057)
Subtotal, ending balance	2,063,494
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	536,060
Foreign translation adjustment	6,657
Other	2,162
Goodwill, ending balance	1,946,985
Accumulated impairment losses, ending balance	0
Subtotal, ending balance	1,946,985
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	24
Other	0
Goodwill, ending balance	101,293
Accumulated impairment losses, ending balance	0
Subtotal, ending balance	101,293
All Other
Goodwill [Roll Forward]
Goodwill, beginning balance	144,332
Accumulated impairment losses, beginning balance	(130,057)
Subtotal, beginning balance	14,275
Goodwill acquired	941
Foreign translation adjustment	0
Other	0
Goodwill, ending balance	145,273
Accumulated impairment losses, ending balance	(130,057)
Subtotal, ending balance	$ 15,216