Acquisitions - Summary of Purchase Price and Allocation of Purchase Price (Details) - USD ($) $ in Thousands		12 Months Ended
	Aug. 15, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Consideration:
Cash, net of cash acquired		$ 151,586	$ 147,507	$ 58,016
Assumed debt		16,885	7,426	2,360
Earn-outs		3,500	3,200
Allocation of the Purchase Price:
Goodwill			125,705	114,935
Noncontrolling interest		(1,916)	(933)	(3,336)
Animal Hospitals And Laboratory Acquisitions [Member]
Consideration:
Cash, net of cash acquired		147,121	122,803	52,688
Holdbacks		5,040	3,000	1,092
Earn-outs		1,671	2,037	1,285
Fair value of total consideration transferred		170,717	135,266	57,425
Allocation of the Purchase Price:
Tangible assets		11,482	5,902	14,779
Identifiable intangible assets		41,216	22,964	15,001
Goodwill		124,198	110,234	45,665
Notes payable and other liabilities assumed		(2,206)	(115)	(11,084)
Fair value of assets acquired and liabilities assumed		174,690	138,985	64,361
Noncontrolling interest		(2,675)	(1,705)	(6,936)
Notes Receivable From Shareholder For Formation of Noncontrolling Interest		(1,298)	0	0
Fair value of pre-existing investment		$ 0	(2,014)	0
Weighted average amortization period		11 years
Amount of goodwill deducted for income tax purpose		$ 101,600	$ 67,200	$ 15,000
Animal Hospitals And Laboratory Acquisitions [Member] | Customer Relationships [Member]
Allocation of the Purchase Price:
Weighted average amortization period		12 years
Animal Hospitals And Laboratory Acquisitions [Member] | Trademarks [Member]
Allocation of the Purchase Price:
Weighted average amortization period		9 years
Animal Hospitals And Laboratory Acquisitions [Member] | Covenants not-to-compete [Member]
Allocation of the Purchase Price:
Weighted average amortization period		5 years
D.O.G. Enterprises, LLC [Member]
Consideration:
Cash, net of cash acquired	$ 15,174
Assumed debt	323
Holdbacks	1,500
Earn-outs	760
Fair value of total consideration transferred	17,757
Allocation of the Purchase Price:
Tangible assets	637
Identifiable intangible assets	13,420
Goodwill	4,219
Notes payable and other liabilities assumed	(519)
Fair value of assets acquired and liabilities assumed	$ 17,757
Weighted average amortization period	10 years
D.O.G. Enterprises, LLC [Member] | Covenants not-to-compete [Member]
Allocation of the Purchase Price:
Weighted average amortization period	3 years
D.O.G. Enterprises, LLC [Member] | Franchise rights [Member]
Allocation of the Purchase Price:
Weighted average amortization period	10 years
D.O.G. Enterprises, LLC [Member] | Existing Technology [Member]
Allocation of the Purchase Price:
Weighted average amortization period	4 years