Lines of Business (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Lines of Business
External revenue	$ 499,453us-gaap_Revenues	$ 449,507us-gaap_Revenues
Intercompany revenue	0woof_IntercompanyRevenue	0woof_IntercompanyRevenue
Total revenue	499,453us-gaap_SalesRevenueNet	449,507us-gaap_SalesRevenueNet
Direct costs	385,591us-gaap_CostOfGoodsAndServicesSold	348,056us-gaap_CostOfGoodsAndServicesSold
Gross profit	113,862us-gaap_GrossProfit	101,451us-gaap_GrossProfit
Selling, general and administrative expense	44,398	41,440
Operating income (loss) before sale or disposal of assets	69,464	60,011
Net loss (gain) on sale or disposal of assets	335us-gaap_GainLossOnDispositionOfAssets	(1,221)us-gaap_GainLossOnDispositionOfAssets
Operating income (loss)	69,129us-gaap_OperatingIncomeLoss	61,232us-gaap_OperatingIncomeLoss
Depreciation and amortization	19,797	19,767
Property and equipment additions	16,526	16,619
Total assets	2,325,002us-gaap_Assets		2,332,020us-gaap_Assets
Operating Segments [Member] \| Animal Hospital [Member]
Lines of Business
External revenue	393,026	351,588
Intercompany revenue	0	0
Total revenue	393,026	351,588
Direct costs	337,542	302,788
Gross profit	55,484	48,800
Selling, general and administrative expense	11,221	9,128
Operating income (loss) before sale or disposal of assets	44,263	39,672
Net loss (gain) on sale or disposal of assets	294	168
Operating income (loss)	43,969	39,504
Depreciation and amortization	16,072	14,742
Property and equipment additions	12,082	13,068
Total assets	2,037,578		2,021,725
Operating Segments [Member] \| Laboratory [Member]
Lines of Business
External revenue	78,809	74,783
Intercompany revenue	15,163	13,751
Total revenue	93,972	88,534
Direct costs	45,990	45,503
Gross profit	47,982	43,031
Selling, general and administrative expense	8,865	8,018
Operating income (loss) before sale or disposal of assets	39,117	35,013
Net loss (gain) on sale or disposal of assets	6	(71)
Operating income (loss)	39,111	35,084
Depreciation and amortization	2,504	2,535
Property and equipment additions	3,216	1,981
Total assets	294,826		258,550
Operating Segments [Member] \| All Other [Member]
Lines of Business
External revenue	26,533	22,201
Intercompany revenue	7,694	5,920
Total revenue	34,227	28,121
Direct costs	22,803	18,152
Gross profit	11,424	9,969
Selling, general and administrative expense	8,687	8,348
Operating income (loss) before sale or disposal of assets	2,737	1,621
Net loss (gain) on sale or disposal of assets	9	(1,184)
Operating income (loss)	2,728	2,805
Depreciation and amortization	1,152	2,136
Property and equipment additions	800	758
Total assets	85,645		89,596
Corporate, Non-Segment [Member]
Lines of Business
External revenue	0	0
Intercompany revenue	0	0
Total revenue	0	0
Direct costs	0	0
Gross profit	0	0
Selling, general and administrative expense	15,625	15,946
Operating income (loss) before sale or disposal of assets	(15,625)	(15,946)
Net loss (gain) on sale or disposal of assets	26	(134)
Operating income (loss)	(15,651)	(15,812)
Depreciation and amortization	592	819
Property and equipment additions	1,064	1,411
Total assets	273,051		270,414
Eliminations [Member]
Lines of Business
External revenue	1,085	935
Intercompany revenue	(22,857)	(19,671)
Total revenue	(21,772)	(18,736)
Direct costs	(20,744)	(18,387)
Gross profit	(1,028)	(349)
Selling, general and administrative expense	0	0
Operating income (loss) before sale or disposal of assets	(1,028)	(349)
Net loss (gain) on sale or disposal of assets	0	0
Operating income (loss)	(1,028)	(349)
Depreciation and amortization	(523)	(465)
Property and equipment additions	(636)	(599)
Total assets	$ (366,098)		$ (308,265)

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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