Goodwill (Details) - USD ($)		3 Months Ended		12 Months Ended
	Oct. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Roll Forward]
Goodwill beginning balance				$ 1,545,918,000	$ 1,442,045,000
Accumulated impairment losses beginning balance				(130,057,000)	(120,811,000)
Goodwill, subtotal beginning balance				1,415,861,000	1,321,234,000
Goodwill acquired					125,705,000	$ 114,935,000
Goodwill impairment	$ 0				0	(9,246,000)
Foreign translation adjustment					(22,527,000)	(9,770,000)
Other					(1,389,000)	(1,292,000)
Goodwill ending balance				1,647,707,000	1,545,918,000	1,442,045,000
Accumulated impairment losses ending balance				(130,057,000)	(130,057,000)	(120,811,000)
Goodwill, subtotal ending balance				$ 1,517,650,000	1,415,861,000	1,321,234,000
Weighted average cost of capital (percent)				14.00%
Animal Hospital [Member]
Goodwill [Roll Forward]
Goodwill beginning balance				$ 1,305,558,000	1,206,213,000
Accumulated impairment losses beginning balance				0	0
Goodwill, subtotal beginning balance				1,305,558,000	1,206,213,000
Goodwill acquired					120,374,000	110,207,000
Goodwill impairment					0	0
Foreign translation adjustment					(22,441,000)	(9,722,000)
Other					(1,385,000)	(1,140,000)
Goodwill ending balance				1,402,106,000	1,305,558,000	1,206,213,000
Accumulated impairment losses ending balance				0	0	0
Goodwill, subtotal ending balance				1,402,106,000	1,305,558,000	1,206,213,000
Laboratory [Member]
Goodwill [Roll Forward]
Goodwill beginning balance				97,535,000	97,556,000
Accumulated impairment losses beginning balance				0	0
Goodwill, subtotal beginning balance				97,535,000	97,556,000
Goodwill acquired					3,824,000	27,000
Goodwill impairment					0	0
Foreign translation adjustment					(86,000)	(48,000)
Other					(4,000)	0
Goodwill ending balance				101,269,000	97,535,000	97,556,000
Accumulated impairment losses ending balance				0	0	0
Goodwill, subtotal ending balance				101,269,000	97,535,000	97,556,000
All Other [Member]
Goodwill [Roll Forward]
Goodwill beginning balance				142,825,000	138,276,000
Accumulated impairment losses beginning balance				(130,057,000)	(120,811,000)
Goodwill, subtotal beginning balance				12,768,000	17,465,000
Goodwill acquired					1,507,000	4,701,000
Goodwill impairment		$ 0				(9,246,000)
Foreign translation adjustment					0	0
Other					0	(152,000)
Goodwill ending balance				144,332,000	142,825,000	138,276,000
Accumulated impairment losses ending balance				(130,057,000)	(130,057,000)	(120,811,000)
Goodwill, subtotal ending balance				$ 14,275,000	$ 12,768,000	$ 17,465,000
Vetstreet [Member] | Operating Segments [Member]
Goodwill [Roll Forward]
Goodwill impairment			$ (9,200,000)