Acquisitions - Animal Hospital Acquisitions (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Consideration:
Cash, net of cash acquired	$ 123,852	$ 540,878
Earn-outs	8,700		$ 9,200
Allocation of the Purchase Price:
Goodwill	2,264,265		$ 2,164,422
Animal Hospitals, Excluding CAPNA
Consideration:
Cash	123,889	188,329
Cash acquired	(37)	(970)
Cash, net of cash acquired	123,852	187,359
Assumed debt	9,697	2,601
Holdbacks	2,255	4,148
Earn-outs	596	4,002
Fair value of total consideration transferred	136,400	198,110
Allocation of the Purchase Price:
Tangible assets	11,086	21,521
Identifiable intangible assets	16,560	24,325
Goodwill	109,090	153,012
Other liabilities assumed	(336)	(437)
Fair value of assets acquired and liabilities assumed	136,400	198,421
Noncontrolling interest	0	(311)
Total	$ 136,400	198,110
Weighted average amortization period	5 years
Goodwill recorded for acquisitions, fully deductible for income tax purposes	$ 99,800	$ 146,900
Animal Hospitals, Excluding CAPNA | Customer Relationships
Allocation of the Purchase Price:
Weighted average amortization period	5 years
Animal Hospitals, Excluding CAPNA | Trademarks
Allocation of the Purchase Price:
Weighted average amortization period	7 years
Animal Hospitals, Excluding CAPNA | Covenants
Allocation of the Purchase Price:
Weighted average amortization period	5 years