Goodwill and Other Long-Lived Assets - Changes in Carrying Amount of Goodwill (Details) $ in Thousands	3 Months Ended
	Mar. 31, 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	129,366
Foreign translation adjustment	9,044
Other	329
Goodwill, ending balance	1,786,446
Accumulated impairment losses, ending balance	130,057
Subtotal, ending balance	1,656,389
Animal Hospital [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	1,402,106
Accumulated impairment losses, beginning balance	0
Subtotal, beginning balance	1,402,106
Goodwill acquired	129,246
Foreign translation adjustment	9,013
Other	329
Goodwill, ending balance	1,540,694
Accumulated impairment losses, ending balance	0
Subtotal, ending balance	1,540,694
Laboratory [Member]
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	31
Other	0
Goodwill, ending balance	101,300
Accumulated impairment losses, ending balance	0
Subtotal, ending balance	101,300
All Other [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	144,332
Accumulated impairment losses, beginning balance	130,057
Subtotal, beginning balance	14,275
Goodwill acquired	120
Foreign translation adjustment	0
Other	0
Goodwill, ending balance	144,452
Accumulated impairment losses, ending balance	130,057
Subtotal, ending balance	$ 14,395