Acquisitions - Companion Animal Practices, North America Acquisition (Details) $ in Thousands		6 Months Ended
	May 01, 2016 USD ($) State Hospital	Jun. 30, 2017 USD ($) State Hospital	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Number of hospitals operated | Hospital		812
Number of states in which hospitals are operated | State		43
Consideration:
Cash, net of cash acquired		$ 123,852	$ 540,878
Allocation of the Purchase Price:
Goodwill		2,264,265		$ 2,164,422
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	$ 352,829
Cash acquired	(3,405)
Cash, net of cash acquired	349,424
Holdbacks	1,000
Fair value of total consideration transferred	350,424
Allocation of the Purchase Price:
Tangible assets	36,381
Identifiable intangible assets	102,300
Goodwill	325,517
Other liabilities assumed	(27,774)
Fair value of assets acquired and liabilities assumed	436,424
Noncontrolling interest	(86,000)
Total	$ 350,424
Weighted average amortization period	7 years
Goodwill recorded for acquisitions, fully deductible for income tax purposes		$ 262,200
Companion Animal Practices, North America | Customer Relationships
Allocation of the Purchase Price:
Weighted average amortization period	7 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