Goodwill and Other Intangible Assets (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Goodwill
Goodwill, Beginning Balance			$ 1,092,480
Goodwill acquired			163,552
Other			(1,971)
Goodwill, Ending Balance	1,254,061		1,254,061
Other Intangible Assets
Gross Carrying Amount	126,892		126,892		74,604
Accumulated Amortization	(32,820)		(32,820)		(27,618)
Net Carrying Amount	94,072		94,072		46,986
Aggregate amortization expense
Aggregate amortization expense	3,833	2,484	9,092	6,825
Estimated amortization expense related to intangible assets
Remainder of 2011			4,403
2012			16,952
2013			14,680
2014			12,348
2015			10,492
Thereafter			35,197
Total			94,072
Goodwill and Other Intangible Assets (Textuals) [Abstract]
Accumulated impairment losses	0		0
Animal Hospital [Member]
Goodwill
Goodwill, Beginning Balance			965,999
Goodwill acquired			64,459
Other			(1,807)
Goodwill, Ending Balance	1,028,651		1,028,651
Laboratory [Member]
Goodwill
Goodwill, Beginning Balance			96,818
Goodwill acquired			6
Other			(30)
Goodwill, Ending Balance	96,794		96,794
All Other [Member]
Goodwill
Goodwill, Beginning Balance			29,663
Goodwill acquired			99,087
Other			(134)
Goodwill, Ending Balance	128,616		128,616
Noncontractual customer relationships [Member]
Other Intangible Assets
Gross Carrying Amount	80,613		80,613		48,686
Accumulated Amortization	(18,297)		(18,297)		(14,188)
Net Carrying Amount	62,316		62,316		34,498
Covenants not-to-compete [Member]
Other Intangible Assets
Gross Carrying Amount	12,990		12,990		14,459
Accumulated Amortization	(8,030)		(8,030)		(8,311)
Net Carrying Amount	4,960		4,960		6,148
Favorable lease asset [Member]
Other Intangible Assets
Gross Carrying Amount	5,571		5,571		5,486
Accumulated Amortization	(3,076)		(3,076)		(2,672)
Net Carrying Amount	2,495		2,495		2,814
Trademarks [Member]
Other Intangible Assets
Gross Carrying Amount	7,545		7,545		3,749
Accumulated Amortization	(1,463)		(1,463)		(986)
Net Carrying Amount	6,082		6,082		2,763
Contracts [Member]
Other Intangible Assets
Gross Carrying Amount	3,500		3,500
Accumulated Amortization	(74)		(74)
Net Carrying Amount	3,426		3,426
Technology [Member]
Other Intangible Assets
Gross Carrying Amount	16,589		16,589		2,189
Accumulated Amortization	(1,852)		(1,852)		(1,447)
Net Carrying Amount	14,737		14,737		742
Client lists [Member]
Other Intangible Assets
Gross Carrying Amount	84		84		35
Accumulated Amortization	(28)		(28)		(14)
Net Carrying Amount	$ 56		$ 56		$ 21