Acquisitions (Details) $ in Thousands			6 Months Ended
		Aug. 15, 2014 USD ($)	Jun. 30, 2015 USD ($) Laboratory Hospital	Jun. 30, 2014 USD ($) Laboratory Hospital	Dec. 31, 2014 USD ($)
Consideration:
Cash, net of cash acquired			$ 66,529	$ 30,764
Earn-out contingent consideration			3,100		$ 3,200
Allocation of the Purchase Price:
Goodwill			1,452,370		$ 1,415,861
Animal Hospitals And Laboratory Acquisitions [Member]
Consideration:
Cash, net of cash acquired			66,229	30,764
Assumed debt			6,250	736
Holdbacks			2,522	750
Earn-out contingent consideration			0	374
Fair value of total consideration transferred			75,001	32,624
Allocation of the Purchase Price:
Tangible assets			5,064	2,688
Identifiable intangible assets	[1]		24,144	4,880
Goodwill	[2]		46,440	26,761
Other liabilities assumed			(647)	0
Fair value of assets acquired			75,001	34,329
Noncontrolling interest			0	(1,705)
Total			$ 75,001	32,624
Weighted average useful life (in years)			15 years
Goodwill recorded for acquisitions, fully deductible for income tax purposes			$ 35,800	$ 16,300
Animal Hospital [Member]
Business Acquisition Summary Of Acquired Properties [Line Items]
Acquisitions | Hospital			23	10
Acquisitions, merged | Hospital			(2)	(2)
Sold, closed or merged | Hospital			(7)	(5)
Net increase | Hospital			14	3
Laboratories Acquisitions [Member]
Business Acquisition Summary Of Acquired Properties [Line Items]
Acquisitions | Laboratory			1	0
Acquisitions, merged | Laboratory			(1)	0
New facilities | Laboratory			0	3
Net increase | Laboratory			0	3
D.O.G. Enterprises, LLC [Member]
Consideration:
Cash, net of cash acquired		$ 15,174
Assumed debt		323
Holdbacks		1,500
Earn-out contingent consideration		760
Fair value of total consideration transferred		17,757
Allocation of the Purchase Price:
Tangible assets		637
Identifiable intangible assets	[3]	13,420
Goodwill	[4]	4,219
Other liabilities assumed		(519)
Total		$ 17,757
Weighted average useful life (in years)		10 years
Customer Relationships [Member] | Animal Hospitals And Laboratory Acquisitions [Member]
Allocation of the Purchase Price:
Weighted average useful life (in years)			16 years
Trademarks [Member] | Animal Hospitals And Laboratory Acquisitions [Member]
Allocation of the Purchase Price:
Weighted average useful life (in years)			8 years
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 fifteen years. The weighted-average amortization period for customer relationships, trademarks and covenants is approximately sixteen years, eight years and five years, respectively.

[2] We expect that $35.8 million and $16.3 million of the goodwill recorded for these acquisitions, as of June 30, 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 June 30, 2015, we expect that the full amount of goodwill recorded for this acquisition will be deductible for income tax purposes.