Acquisition (Details) (USD $)	3 Months Ended				0 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Aug. 15, 2014		Dec. 31, 2014
Consideration:
Cash, net of cash acquired	$ 32,150,000		$ 17,295,000
Earn-out contingent consideration	3,000,000						3,200,000
Allocation of the Purchase Price:
Goodwill	1,439,598,000						1,415,861,000
Animal Hospitals And Laboratory Acquisitions [Member]
Consideration:
Cash, net of cash acquired	31,850,000		17,295,000
Assumed debt	4,446,000		0
Holdbacks	1,722,000		400,000
Fair value of total consideration transferred	38,018,000		17,695,000
Allocation of the Purchase Price:
Tangible assets	764,000		701,000
Identifiable intangible assets	2,838,000	[1]	2,734,000	[1]
Goodwill	34,563,000	[2]	15,115,000	[2]
Other liabilities assumed	(147,000)		0
Fair value of assets acquired	38,018,000		18,550,000
Noncontrolling interest	0		(855,000)
Total	38,018,000		17,695,000
Weighted average useful life (in years)	5 years
Goodwill recorded for acquisitions, fully deductible for income tax purposes	30,600,000		10,300,000
Animal Hospital [Member]
Business Acquisition Summary Of Acquired Properties [Line Items]
Acquisitions	11		4
Acquisitions, merged	(2)		(1)
Sold, closed or merged	(2)		(4)
Net increase (decrease)	7		(1)
Laboratories Acquisitions [Member]
Business Acquisition Summary Of Acquired Properties [Line Items]
Acquisitions	1		0
Acquisitions, merged	(1)		0
New facilities	0		1
Net increase	0		1
D.O.G. Enterprises, LLC [Member]
Consideration:
Cash, net of cash acquired					15,174,000
Assumed debt					323,000
Holdbacks					1,500,000
Earn-out contingent consideration					760,000
Fair value of total consideration transferred					17,757,000
Allocation of the Purchase Price:
Tangible assets					637,000
Identifiable intangible assets					13,420,000	[3]
Goodwill					4,219,000	[4]
Other liabilities assumed					(519,000)
Total					$ 17,757,000
Weighted average useful life (in years)					10 years
Customer Relationships, Trademarks and Covenants [Member] | Animal Hospitals And Laboratory Acquisitions [Member]
Allocation of the Purchase Price:
Weighted average useful life (in years)	5 years
Covenants [Member] | D.O.G. Enterprises, LLC [Member]
Allocation of the Purchase Price:
Weighted average useful life (in years)					3 years
Franchise rights [Member] | D.O.G. Enterprises, LLC [Member]
Allocation of the Purchase Price:
Weighted average useful life (in years)					10 years
Existing Technology [Member] | D.O.G. Enterprises, LLC [Member]
Allocation of the Purchase Price:
Weighted average useful life (in years)					4 years

[1] Identifiable intangible assets include customer relationships, trademarks and covenants-not-to-compete. The weighted-average amortization period for the total identifiable intangible assets is approximately five years. The weighted-average amortization period for customer relationships, trademarks and covenants is approximately five years.

[2] We expect that $30.6 million and $10.3 million of the goodwill recorded for these acquisitions, as of March 31, 2015 and 2014, respectively, will be fully deductible for income tax purposes.

[3] Identifiable intangible assets primarily include franchise rights, trademarks, covenants-not-to-compete and existing technology. The weighted-average amortization period for the total identifiable intangible assets is approximately ten years. The weighted-average amortization periods for the franchise rights, covenants and existing technology is approximately ten years, three years and four years, respectively. The trademarks have an indefinite life and will be assessed annually for impairment.

[4] As of March 31, 2015, we expect that the full amount of goodwill recorded for this acquisition will be deductible for income tax purposes.