Acquisitions - Companion Animal Practices, North America Acquisition (Details) $ in Thousands		8 Months Ended	12 Months Ended
	May 01, 2016 USD ($) State Hospital	Dec. 31, 2016 USD ($) State Hospital	Dec. 31, 2016 USD ($) State Hospital	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Number of hospitals operated | Hospital		795	795
Number of states in which hospitals are operated | State		43	43
Consideration:
Cash, net of cash acquired			$ 697,673	$ 151,586	$ 147,507
Allocation of the Purchase Price:
Goodwill		$ 2,164,422	$ 2,164,422	1,517,650	1,415,861
Weighted average amortization period			5 years
Amount of goodwill deducted for income tax purpose		263,400	$ 263,400	$ 100,100	$ 62,500
Customer Relationships
Allocation of the Purchase Price:
Weighted average amortization period			5 years
Trademarks
Allocation of the Purchase Price:
Weighted average amortization period			8 years
Noncompete Agreements
Allocation of the Purchase Price:
Weighted average amortization period			5 years
Companion Animal Practices, North America
Business Acquisition [Line Items]
Percentage of Company acquired	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	5,400
Allocation of the Purchase Price:
Tangible assets	25,063
Identifiable intangible assets	102,300
Goodwill	336,950
Other liabilities assumed	(27,889)
Fair value of assets acquired and liabilities assumed	436,424
Noncontrolling interest	(86,000)
Total	$ 350,424
Weighted average amortization period	7 years
Amount of goodwill deducted for income tax purpose		$ 270,300	$ 270,300
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 | Noncompete Agreements
Allocation of the Purchase Price:
Weighted average amortization period	5 years