Lines of Business (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Lines of Business
External revenue	$ 449,507	$ 438,606
Intercompany revenue	0	0
Total revenue	449,507	438,606
Direct costs	348,056	341,683
Gross profit	101,451	96,923
Selling, general and administrative expense	41,440	39,846
Operating income (loss) before sale or disposal of assets	60,011	57,077
Net loss (gain) on sale or disposal of assets	(1,221)	1,726
Operating income	61,232	55,351
Depreciation and amortization	19,767	18,239
Capital expenditures	16,619	17,969
Total assets	2,249,931		2,237,781
Intersegment Eliminations [Member]
Lines of Business
External revenue	935	725
Intercompany revenue	(19,671)	(18,592)
Total revenue	(18,736)	(17,867)
Direct costs	(18,387)	(17,492)
Gross profit	(349)	(375)
Selling, general and administrative expense	0	0
Operating income (loss) before sale or disposal of assets	(349)	(375)
Net loss (gain) on sale or disposal of assets	0	0
Operating income	(349)	(375)
Depreciation and amortization	(465)	(439)
Capital expenditures	(599)	(363)
Total assets	(40,431)		(37,817)
Operating Segments [Member] | Animal Hospital [Member]
Lines of Business
External revenue	351,588	340,615
Intercompany revenue	0	0
Total revenue	351,588	340,615
Direct costs	302,788	295,416
Gross profit	48,800	45,199
Selling, general and administrative expense	9,128	8,325
Operating income (loss) before sale or disposal of assets	39,672	36,874
Net loss (gain) on sale or disposal of assets	168	1,729
Operating income	39,504	35,145
Depreciation and amortization	14,742	13,387
Capital expenditures	13,068	14,441
Total assets	1,864,993		1,854,609
Operating Segments [Member] | Laboratory [Member]
Lines of Business
External revenue	74,783	73,638
Intercompany revenue	13,751	13,697
Total revenue	88,534	87,335
Direct costs	45,503	44,870
Gross profit	43,031	42,465
Selling, general and administrative expense	8,018	8,005
Operating income (loss) before sale or disposal of assets	35,013	34,460
Net loss (gain) on sale or disposal of assets	(71)	(5)
Operating income	35,084	34,465
Depreciation and amortization	2,535	2,507
Capital expenditures	1,981	1,918
Total assets	261,178		247,591
Operating Segments [Member] | All Other Segments [Member]
Lines of Business
External revenue	22,201	23,628
Intercompany revenue	5,920	4,895
Total revenue	28,121	28,523
Direct costs	18,152	18,889
Gross profit	9,969	9,634
Selling, general and administrative expense	8,348	8,914
Operating income (loss) before sale or disposal of assets	1,621	720
Net loss (gain) on sale or disposal of assets	(1,184)	2
Operating income	2,805	718
Depreciation and amortization	2,136	1,965
Capital expenditures	758	1,333
Total assets	94,145		96,245
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	15,946	14,602
Operating income (loss) before sale or disposal of assets	(15,946)	(14,602)
Net loss (gain) on sale or disposal of assets	(134)	0
Operating income	(15,812)	(14,602)
Depreciation and amortization	819	819
Capital expenditures	1,411	640
Total assets	$ 70,046		$ 77,153