Lines of Business (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenue from Related Parties									$ 0	$ 0	$ 0
External revenue									1,803,369	1,699,642	1,485,361
Revenue, Net	435,453	464,055	465,255	438,606	418,192	433,613	438,372	409,465	1,803,369	1,699,642	1,485,361
Gross Profit	87,486	110,677	114,294	96,923	81,807	99,181	100,607	93,379	409,380	374,974	338,457
Direct costs									1,393,989	1,324,668	1,146,904
Selling, General and Administrative Expense									157,911	157,155	121,112
Operating income before significant charges									251,469	217,819	217,345
Goodwill, Impairment Loss					123,600					99,501	21,310
Goodwill and Intangible Asset Impairment										(123,573)
Asset Impairment Charges									0
Gain (Loss) on Disposition of Assets									2,455	1,310	382
Disclosure on Geographic Areas, Description of Revenue from External Customers									*Revenues are determined based on the location of the customer.
Operating income (loss)	45,923	72,039	75,701	55,351	(83,553)	61,186	61,498	53,805	249,014	92,936	195,653
Disclosure on Geographic Areas, Revenue from External Customers Attributed to Entity's Country of Domicile									1,803,369	1,699,642	1,485,361
Assets	2,237,781				2,091,580				2,237,781	2,091,580	1,995,368
Depreciation and amortization									77,409	76,227	56,988
Payments to Acquire Property, Plant, and Equipment									73,270	76,807	63,485
Animal Hospital [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									0	0	0
External revenue									1,417,908	1,331,314	1,150,120
Revenue, Net									1,417,908	1,331,314	1,150,120
Gross Profit									209,127	189,111	179,810
Direct costs									1,208,781	1,142,203	970,310
Selling, General and Administrative Expense									34,133	30,826	24,342
Operating income before significant charges									174,994	158,285	155,468
Goodwill, Impairment Loss										0	0
Goodwill and Intangible Asset Impairment										(1,216)
Gain (Loss) on Disposition of Assets									2,853	713	327
Operating income (loss)									172,141	156,356	155,141
Disclosure on Geographic Areas, Revenue from External Customers Attributed to Entity's Country of Domicile									1,417,908	1,331,314	1,150,120
Assets	1,854,609				1,648,578				1,854,609	1,648,578	1,439,103
Depreciation and amortization									57,748	54,835	40,319
Payments to Acquire Property, Plant, and Equipment									54,116	55,651	45,753
Laboratory [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									54,248	52,395	44,329
External revenue									290,583	275,406	272,468
Revenue, Net									344,831	327,801	316,797
Gross Profit									163,879	151,761	143,790
Direct costs									180,952	176,040	173,007
Selling, General and Administrative Expense									31,915	29,660	27,864
Operating income before significant charges									131,964	122,101	115,926
Goodwill, Impairment Loss										0	0
Goodwill and Intangible Asset Impairment										0
Gain (Loss) on Disposition of Assets									(77)	(14)	21
Operating income (loss)									132,041	122,115	115,905
Disclosure on Geographic Areas, Revenue from External Customers Attributed to Entity's Country of Domicile									290,583	275,406	272,468
Assets	247,591				244,551				247,591	244,551	232,423
Depreciation and amortization									10,251	10,141	10,111
Payments to Acquire Property, Plant, and Equipment									11,148	8,334	6,082
Other Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									21,054	22,344	18,694
External revenue									91,686	90,616	61,736
Revenue, Net									112,740	112,960	80,430
Gross Profit									38,601	38,707	20,971
Direct costs									74,139	74,253	59,459
Selling, General and Administrative Expense									32,941	37,879	19,136
Operating income before significant charges									5,660	828	1,835
Goodwill, Impairment Loss										99,501	21,310
Goodwill and Intangible Asset Impairment										(122,357)
Gain (Loss) on Disposition of Assets									7	717	27
Operating income (loss)									5,653	(122,246)	(19,502)
Disclosure on Geographic Areas, Revenue from External Customers Attributed to Entity's Country of Domicile									91,686	90,616	61,736
Assets	96,245				98,159				96,245	98,159	202,187
Depreciation and amortization									7,909	9,582	5,022
Payments to Acquire Property, Plant, and Equipment									4,288	5,921	6,448
Corporate [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									0	0	0
External revenue									0	0	0
Revenue, Net									0	0	0
Gross Profit									0	0	0
Direct costs									0	0	0
Selling, General and Administrative Expense									58,922	58,790	49,770
Operating income before significant charges									(58,922)	(58,790)	(49,770)
Goodwill, Impairment Loss											0
Goodwill and Intangible Asset Impairment										0
Gain (Loss) on Disposition of Assets									(328)	(106)	7
Operating income (loss)									(58,594)	(58,684)	(49,777)
Disclosure on Geographic Areas, Revenue from External Customers Attributed to Entity's Country of Domicile									0	0	0
Assets	77,153				127,963				77,153	127,963	142,793
Depreciation and amortization									3,284	3,198	2,853
Payments to Acquire Property, Plant, and Equipment									5,908	9,695	7,299
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenue from Related Parties									(75,302)	(74,739)	(63,023)
External revenue									3,192	2,306	1,037
Revenue, Net									(72,110)	(72,433)	(61,986)
Gross Profit									(2,227)	(4,605)	(6,114)
Direct costs									(69,883)	(67,828)	(55,872)
Selling, General and Administrative Expense									0	0	0
Operating income before significant charges									(2,227)	(4,605)	(6,114)
Goodwill, Impairment Loss											0
Goodwill and Intangible Asset Impairment										0
Gain (Loss) on Disposition of Assets									0	0	0
Operating income (loss)									(2,227)	(4,605)	(6,114)
Disclosure on Geographic Areas, Revenue from External Customers Attributed to Entity's Country of Domicile									3,192	2,306	1,037
Assets	(37,817)				(27,671)				(37,817)	(27,671)	(21,138)
Depreciation and amortization									(1,783)	(1,529)	(1,317)
Payments to Acquire Property, Plant, and Equipment									(2,190)	(2,794)	(2,097)
UNITED STATES
Segment Reporting Information [Line Items]
External revenue									1,671,170	1,589,588	1,474,294
Disclosure on Geographic Areas, Revenue from External Customers Attributed to Entity's Country of Domicile									1,671,170	1,589,588	1,474,294
CANADA
Segment Reporting Information [Line Items]
External revenue									132,199	110,054	11,067
Disclosure on Geographic Areas, Revenue from External Customers Attributed to Entity's Country of Domicile									$ 132,199	$ 110,054	$ 11,067