Acquisitions (Details Textuals) (USD $)	3 Months Ended	9 Months Ended			3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Animal Hospitals and Laboratory Acquisitions [Member]	Sep. 30, 2011 Bright Heart [Member]	Sep. 30, 2011 Bright Heart [Member] Year Hospital	Jul. 11, 2011 Bright Heart [Member]	Sep. 30, 2011 Vetstreet [Member]	Sep. 30, 2011 Vetstreet [Member] Year	Aug. 09, 2011 Vetstreet [Member]	Sep. 30, 2011 Vetstreet [Member] Customer Relationships [Member] Year	Sep. 30, 2011 Vetstreet [Member] Technology and Trademarks [Member] Year	Sep. 30, 2011 Vetstreet [Member] Non-compete Agreements [Member] Year	Sep. 30, 2011 Vetstreet [Member] Contracts [Member] Year
Acquisitions (Textuals) [Abstract]
Acquisition-related costs (included in corporate selling, general and administrative expense in our income statement for the three and nine months ended September 30, 2011	$ 1,500,000	$ 2,000,000	$ 2,000,000		$ 851,000	$ 1,100,000		$ 657,000	$ 911,000
Amount of goodwill deducted for income tax purpose				16,200,000	47,431,000	47,431,000		99,087,000	99,087,000
Cash payments made for real estate acquired through acquisition		1,900,000	5,834,000	1,900,000
Business Acquisition Cost of Acquired Entity Cash Paid	189,255,000	189,255,000	42,827,000	19,499,000	23,490,000	23,490,000	50,000,000	146,420,000	146,420,000
Business acquisition percentage of voting interests acquired					100.00%	100.00%		100.00%	100.00%
Weighted average amortization period						5			9		10	7	2	8
Preliminary purchase price										$ 146,400,000