Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Roll Forward]
Goodwill beginning balance	$ 1,647,707	$ 1,545,918
Accumulated impairment losses beginning balance	(130,057)	(130,057)
Goodwill, subtotal beginning balance	1,517,650	1,415,861
Goodwill acquired		640,877	$ 125,705
Foreign translation adjustment		3,584	(22,527)
Other		2,311	(1,389)
Goodwill ending balance	2,294,479	1,647,707	1,545,918
Accumulated impairment losses ending balance	(130,057)	(130,057)	(130,057)
Goodwill, subtotal ending balance	2,164,422	1,517,650	1,415,861
Animal Hospital
Goodwill [Roll Forward]
Goodwill beginning balance	1,402,106	1,305,558
Accumulated impairment losses beginning balance	0	0
Goodwill, subtotal beginning balance	1,402,106	1,305,558
Goodwill acquired		639,907	120,374
Foreign translation adjustment		3,570	(22,441)
Other		2,311	(1,385)
Goodwill ending balance	2,047,894	1,402,106	1,305,558
Accumulated impairment losses ending balance	0	0	0
Goodwill, subtotal ending balance	2,047,894	1,402,106	1,305,558
Laboratory
Goodwill [Roll Forward]
Goodwill beginning balance	101,269	97,535
Accumulated impairment losses beginning balance	0	0
Goodwill, subtotal beginning balance	101,269	97,535
Goodwill acquired		0	3,824
Foreign translation adjustment		14	(86)
Other		0	(4)
Goodwill ending balance	101,283	101,269	97,535
Accumulated impairment losses ending balance	0	0	0
Goodwill, subtotal ending balance	101,283	101,269	97,535
All Other
Goodwill [Roll Forward]
Goodwill beginning balance	144,332	142,825
Accumulated impairment losses beginning balance	(130,057)	(130,057)
Goodwill, subtotal beginning balance	14,275	12,768
Goodwill acquired		970	1,507
Foreign translation adjustment		0	0
Other		0	0
Goodwill ending balance	145,302	144,332	142,825
Accumulated impairment losses ending balance	(130,057)	(130,057)	(130,057)
Goodwill, subtotal ending balance	$ 15,245	$ 14,275	$ 12,768