Acquisitions (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consideration:
Cash paid for acquisitions		$ (203,996)	$ (79,851)
Contingent consideration	1,306	560	259
Allocation of the Purchase Price:
Noncontrolling Interest, Increase from Business Combination	(8,161)	0	0
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value	(11,850)	0	0
Animal Hospitals And Laboratory Acquisitions [Member]
Consideration:
Cash paid for acquisitions	78,629	34,243	69,456
Contingent consideration	1,306	79	2,857
Cash paid for holdbacks	2,425	1,500	0
Fair value of total consideration transferred	82,360	35,822	72,313
Allocation of the Purchase Price:
Tangible assets	3,515	1,237	3,592
Identifiable intangible assets	14,718	6,414	9,510
Goodwill	64,253	28,171	60,839
Notes payable and other liabilities assumed	(126)	0	(1,628)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	82,360	35,822	72,313
Think Pets Inc [Member]
Consideration:
Cash paid for acquisitions	7,468
Cash paid for holdbacks	1,050
Fair value of total consideration transferred	19,018
Allocation of the Purchase Price:
Tangible assets	2,093
Identifiable intangible assets	7,221
Goodwill	12,155
Notes payable and other liabilities assumed	(2,451)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	19,018
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	(10,500)
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	8 years
Animal Hospitals and Laboratory Acquisitions [Member]
Consideration:
Cash paid for acquisitions	48,819
Cash paid to holders of debt	25,915
Fair value of total consideration transferred	74,734
Allocation of the Purchase Price:
Tangible assets	11,694
Identifiable intangible assets	25,170
Goodwill	79,707
Notes payable and other liabilities assumed	(21,826)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	74,734
business acquisition purchase price allocation total	94,745
Noncontrolling Interest, Increase from Business Combination	(8,161)
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value	(11,850)
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	6 years
Pet DRx [Member]
Consideration:
Cash paid to holders of debt			29,532
Cash paid for holdbacks			750
Fair value of total consideration transferred			37,952
Allocation of the Purchase Price:
Tangible assets			20,031
Identifiable intangible assets			3,074
Goodwill			41,686
Notes payable and other liabilities assumed			(26,839)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net			$ 37,952
Customer Relationships [Member] | Think Pets Inc [Member]
Allocation of the Purchase Price:
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	9 years
Customer Relationships [Member] | Animal Hospitals and Laboratory Acquisitions [Member]
Allocation of the Purchase Price:
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years