Lines of Business (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Lines of Business
External revenue	$ 489,472	$ 465,255	$ 938,979	$ 903,861
Intercompany revenue	0	0	0	0
Total revenue	489,472	465,255	938,979	903,861
Direct costs	369,057	350,961	717,113	692,644
Gross profit	120,415	114,294	221,866	211,217
Selling, general and administrative expense	39,931	39,023	81,371	78,869
Operating income (loss) before sale or disposal of assets	80,484	75,271	140,495	132,348
Net (gain) loss on sale or disposal of assets	578	(430)	(643)	1,296
Operating income (loss)	79,906	75,701	141,138	131,052
Depreciation and amortization	20,030	19,500	39,797	37,739
Capital expenditures	11,360	15,126	27,979	33,095
Total assets	2,259,238		2,259,238		2,237,781
Intersegment Eliminations [Member]
Lines of Business
External revenue	919	872	1,854	1,597
Intercompany revenue	(17,890)	(19,524)	(37,561)	(38,116)
Total revenue	(16,971)	(18,652)	(35,707)	(36,519)
Direct costs	(17,310)	(18,184)	(35,697)	(35,676)
Gross profit	339	(468)	(10)	(843)
Selling, general and administrative expense	0	0	0	0
Operating income (loss) before sale or disposal of assets	339	(468)	(10)	(843)
Net (gain) loss on sale or disposal of assets	0	0	0	0
Operating income (loss)	339	(468)	(10)	(843)
Depreciation and amortization	(473)	(446)	(938)	(885)
Capital expenditures	(316)	(363)	(915)	(726)
Total assets	(104,876)		(104,876)		(37,817)
Operating Segments [Member] | Animal Hospital [Member]
Lines of Business
External revenue	386,776	365,205	738,364	705,820
Intercompany revenue	0	0	0	0
Total revenue	386,776	365,205	738,364	705,820
Direct costs	323,440	305,092	626,228	600,508
Gross profit	63,336	60,113	112,136	105,312
Selling, general and administrative expense	9,864	8,720	18,992	17,045
Operating income (loss) before sale or disposal of assets	53,472	51,393	93,144	88,267
Net (gain) loss on sale or disposal of assets	414	(160)	582	1,569
Operating income (loss)	53,058	51,553	92,562	86,698
Depreciation and amortization	15,110	14,684	29,852	28,071
Capital expenditures	8,119	11,326	21,187	25,767
Total assets	1,880,805		1,880,805		1,854,609
Operating Segments [Member] | Laboratory [Member]
Lines of Business
External revenue	81,320	76,949	156,103	150,588
Intercompany revenue	14,635	14,281	28,386	27,977
Total revenue	95,955	91,230	184,489	178,565
Direct costs	46,863	46,004	92,366	90,874
Gross profit	49,092	45,226	92,123	87,691
Selling, general and administrative expense	8,281	7,965	16,299	15,970
Operating income (loss) before sale or disposal of assets	40,811	37,261	75,824	71,721
Net (gain) loss on sale or disposal of assets	(7)	(1)	(78)	(6)
Operating income (loss)	40,818	37,262	75,902	71,727
Depreciation and amortization	2,563	2,590	5,098	5,097
Capital expenditures	1,304	1,818	3,285	3,736
Total assets	261,786		261,786		247,591
Operating Segments [Member] | All Other [Member]
Lines of Business
External revenue	20,457	22,229	42,658	45,856
Intercompany revenue	3,255	5,243	9,175	10,139
Total revenue	23,712	27,472	51,833	55,995
Direct costs	16,064	18,049	34,216	36,938
Gross profit	7,648	9,423	17,617	19,057
Selling, general and administrative expense	7,411	8,041	15,759	16,955
Operating income (loss) before sale or disposal of assets	237	1,382	1,858	2,102
Net (gain) loss on sale or disposal of assets	97	1	(1,087)	3
Operating income (loss)	140	1,381	2,945	2,099
Depreciation and amortization	2,004	1,937	4,140	3,902
Capital expenditures	920	1,039	1,678	2,372
Total assets	87,548		87,548		96,245
Corporate, Non-Segment [Member]
Lines of Business
External revenue	0	0	0	0
Intercompany revenue	0	0	0	0
Total revenue	0	0	0	0
Direct costs	0	0	0	0
Gross profit	0	0	0	0
Selling, general and administrative expense	14,375	14,297	30,321	28,899
Operating income (loss) before sale or disposal of assets	(14,375)	(14,297)	(30,321)	(28,899)
Net (gain) loss on sale or disposal of assets	74	(270)	(60)	(270)
Operating income (loss)	(14,449)	(14,027)	(30,261)	(28,629)
Depreciation and amortization	826	735	1,645	1,554
Capital expenditures	1,333	1,306	2,744	1,946
Total assets	$ 133,975		$ 133,975		$ 77,153