Summary of Significant Accounting Policies (Details 3) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Goodwill
Goodwill, Beginning Balance	$ 1,237,607	$ 1,092,480
Goodwill acquired	156,115	167,352
Goodwill impairment	(99,501)	(21,310)	0
Other	(4,288)	(901)
Goodwill, Ending Balance	1,291,231	1,237,607	1,092,480
Goodwill, Impaired, Accumulated Impairment Loss	(120,811)	21,310	0
Animal Hospital [Member]
Goodwill
Goodwill, Beginning Balance	1,035,401	965,999
Goodwill acquired	143,926	70,169
Goodwill impairment	0	0
Other	(3,260)	(767)
Goodwill, Ending Balance	1,177,348	1,035,401
Goodwill, Impaired, Accumulated Impairment Loss	0	0	0
Laboratory [Member]
Goodwill
Goodwill, Beginning Balance	96,810	96,818
Goodwill acquired	34	6
Goodwill impairment	0	0
Other	0	0
Goodwill, Ending Balance	96,861	96,810
Goodwill, Impaired, Accumulated Impairment Loss	$ 0	$ 0	$ 0