Acquisitions - Animal Hospital Acquisitions (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Consideration:
Cash, net of cash acquired	$ 81,721	$ 160,385
Earn-outs	8,600		$ 9,200
Allocation of the Purchase Price:
Goodwill	2,228,189		$ 2,164,422
Animal Hospital
Consideration:
Cash, net of cash acquired	81,721	157,325
Assumed debt	8,374	1,361
Holdbacks	1,600	3,508
Earn-outs	0	3,437
Fair value of total consideration transferred	91,695	165,631
Allocation of the Purchase Price:
Tangible assets	5,395	17,541
Identifiable intangible assets	10,303	18,844
Goodwill	75,884	129,246
Other liabilities assumed	113	0
Fair value of assets acquired and liabilities assumed	$ 91,695	165,631
Weighted average amortization period	5 years
Goodwill recorded for acquisitions, fully deductible for income tax purposes	$ 75,900	$ 129,200
Animal Hospital \| Customer Relationships
Allocation of the Purchase Price:
Weighted average amortization period	5 years
Animal Hospital \| Trademarks
Allocation of the Purchase Price:
Weighted average amortization period	2 years
Animal Hospital \| Covenants
Allocation of the Purchase Price:
Weighted average amortization period	5 years

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of other liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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