Acquisitions - Animal Hospital and Laboratory Acquisitions (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Consideration:
Cash, net of cash acquired	$ 540,878	$ 66,529
Earn-outs	6,500		$ 3,500
Allocation of the Purchase Price:
Goodwill	1,963,377		$ 1,517,650
Animal Hospitals And Laboratory Acquisitions
Consideration:
Cash	188,329	66,229
Cash acquired	(970)	0
Cash, net of cash acquired	187,359	66,229
Assumed debt	2,601	6,250
Holdbacks	4,148	2,522
Earn-outs	4,002	0
Fair value of total consideration transferred	198,110	75,001
Allocation of the Purchase Price:
Tangible assets	21,521	5,064
Identifiable intangible assets	24,325	24,144
Goodwill	153,012	46,440
Other liabilities assumed	(437)	(647)
Fair value of assets acquired and liabilities assumed	198,421	75,001
Noncontrolling interest	(311)	0
Total	$ 198,110	75,001
Weighted average amortization period	5 years
Goodwill recorded for acquisitions, fully deductible for income tax purposes	$ 146,900	$ 35,500
Animal Hospitals And Laboratory Acquisitions | Customer Relationships
Allocation of the Purchase Price:
Weighted average amortization period	5 years
Animal Hospitals And Laboratory Acquisitions | Trademarks
Allocation of the Purchase Price:
Weighted average amortization period	7 years
Animal Hospitals And Laboratory Acquisitions | Covenants
Allocation of the Purchase Price:
Weighted average amortization period	5 years