Lines of Business (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Lines of Business
External revenue	$ 438,372	$ 376,105	$ 847,837	$ 731,228
Intercompany revenue	0		0
Total revenue	438,372	376,105	847,837	731,228
Direct costs	337,765	279,273	653,851	554,618
Gross profit	100,607	96,832	193,986	176,610
Selling, general and administrative expense	38,997	26,663	78,048	52,846
Net (gain) loss on sale of assets	112	60	635	149
Operating income (loss)	61,498	70,109	115,303	123,615
Depreciation and amortization	20,801	13,076	37,363	26,456
Property and equipment additions	21,093	16,400	37,165	28,434
Total assets	2,151,195		2,151,195		1,995,368
Animal Hospital [Member]
Lines of Business
External revenue	342,282	291,332	658,407	561,273
Intercompany revenue	0		0
Total revenue	342,282	291,332	658,407	561,273
Direct costs	292,902	238,392	563,471	468,780
Gross profit	49,380	52,940	94,936	92,493
Selling, general and administrative expense	7,995	6,044	15,052	12,127
Net (gain) loss on sale of assets	(112)	51	393	129
Operating income (loss)	41,497	46,845	79,491	80,237
Depreciation and amortization	15,239	9,533	26,583	19,406
Property and equipment additions	15,297	13,236	26,063	22,771
Total assets	1,578,725		1,578,725		1,439,103
Laboratory [Member]
Lines of Business
External revenue	72,452	72,955	144,423	142,051
Intercompany revenue	14,168	11,430	26,927	21,883
Total revenue	86,620	84,385	171,350	163,934
Direct costs	44,324	43,716	88,503	86,535
Gross profit	42,296	40,669	82,847	77,399
Selling, general and administrative expense	7,510	6,853	15,108	13,489
Net (gain) loss on sale of assets	(7)	7	(14)	18
Operating income (loss)	34,793	33,809	67,753	63,892
Depreciation and amortization	2,521	2,508	5,074	4,979
Property and equipment additions	2,282	1,728	3,349	2,964
Total assets	244,360		244,360		232,423
All Other [Member]
Lines of Business
External revenue	23,638	11,818	45,007	27,904
Intercompany revenue	3,780	4,391	8,736	7,401
Total revenue	27,418	16,209	53,743	35,305
Direct costs	17,624	11,419	35,282	26,057
Gross profit	9,794	4,790	18,461	9,248
Selling, general and administrative expense	9,029	3,584	18,312	7,140
Net (gain) loss on sale of assets	232	2	240	2
Operating income (loss)	533	1,204	(91)	2,106
Depreciation and amortization	2,582	668	4,845	1,325
Property and equipment additions	1,048	258	2,770	1,017
Total assets	219,390		219,390		202,187
Corporate [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	14,463	10,182	29,576	20,090
Net (gain) loss on sale of assets	(1)		16
Operating income (loss)	(14,462)	(10,182)	(29,592)	(20,090)
Depreciation and amortization	804	685	1,568	1,365
Property and equipment additions	3,008	1,627	5,991	2,585
Total assets	132,700		132,700		142,793
Intercompany Eliminations [Member]
Lines of Business
External revenue	0		0
Intercompany revenue	(17,948)	(15,821)	(35,663)	(29,284)
Total revenue	(17,948)	(15,821)	(35,663)	(29,284)
Direct costs	(17,085)	(14,254)	(33,405)	(26,754)
Gross profit	(863)	(1,567)	(2,258)	(2,530)
Selling, general and administrative expense	0		0
Net (gain) loss on sale of assets	0		0
Operating income (loss)	(863)	(1,567)	(2,258)	(2,530)
Depreciation and amortization	(345)	(318)	(707)	(619)
Property and equipment additions	(542)	(449)	(1,008)	(903)
Total assets	$ (23,980)		$ (23,980)		$ (21,138)