Goodwill (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill [Line Items]
Goodwill	$ 1,545,918	$ 1,442,045	$ 1,402,401
Accumulated Impairment losses	(130,057)	(120,811)	(120,811)
Goodwill, subtotal	1,415,861	1,321,234	1,281,590
Goodwill acquired		114,935	45,665
Impairment of goodwill and other long-lived assets		(9,246)
Foreign translation adjustment		(9,770)	(5,691)
Other		(1,292)	(330)
Weighted average cost of capital (percent)	14.00%
Animal Hospital [Member]
Goodwill [Line Items]
Goodwill	1,305,558	1,206,213	1,167,022
Accumulated Impairment losses	0	0	0
Goodwill, subtotal	1,305,558	1,206,213	1,167,022
Goodwill acquired		110,207	45,615
Impairment of goodwill and other long-lived assets		0
Foreign translation adjustment		(9,722)	(5,651)
Other		(1,140)	(773)
Laboratory [Member]
Goodwill [Line Items]
Goodwill	97,535	97,556	97,546
Accumulated Impairment losses	0	0	0
Goodwill, subtotal	97,535	97,556	97,546
Goodwill acquired		27	50
Impairment of goodwill and other long-lived assets		0
Foreign translation adjustment		(48)	(40)
Other		0	0
All Other [Member]
Goodwill [Line Items]
Goodwill	142,825	138,276	137,833
Accumulated Impairment losses	(130,057)	(120,811)	(120,811)
Goodwill, subtotal	12,768	17,465	17,022
Goodwill acquired		4,701	0
Impairment of goodwill and other long-lived assets		(9,246)
Foreign translation adjustment		0	0
Other		$ (152)	$ 443