Acquisitions - Companion Animal Practices, North America Acquisition (Details) $ in Thousands		6 Months Ended
	May 01, 2016 USD ($) Hospital State	Jun. 30, 2016 USD ($) Hospital State	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Number of hospitals operated | Hospital		767
Number of states in which hospitals are operated | State		43
Consideration:
Cash, net of cash acquired		$ 540,878	$ 66,529
Allocation of the Purchase Price:
Goodwill		1,963,377		$ 1,517,650
Companion Animal Practices, North America
Business Acquisition [Line Items]
Percentage of ownership interest	80.00%
Number of hospitals operated | Hospital	56
Number of states in which hospitals are operated | State	18
Consideration:
Cash	$ 353,554
Cash acquired	(3,405)
Cash, net of cash acquired	350,149
Holdbacks	1,000
Fair value of total consideration transferred	351,149
Allocation of the Purchase Price:
Tangible assets	13,548
Identifiable intangible assets	147,500
Goodwill	281,311
Other liabilities assumed	(2,572)
Fair value of assets acquired and liabilities assumed	439,787
Noncontrolling interest	(88,638)
Total	$ 351,149
Weighted average amortization period	9 years
Goodwill recorded for acquisitions, fully deductible for income tax purposes		$ 225,000
Companion Animal Practices, North America | Customer Relationships
Allocation of the Purchase Price:
Weighted average amortization period	10 years
Companion Animal Practices, North America | Trademarks
Allocation of the Purchase Price:
Weighted average amortization period	5 years
Companion Animal Practices, North America | Covenants
Allocation of the Purchase Price:
Weighted average amortization period	5 years