Lines of Business (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Lines of Business
External revenue	$ 548,785	$ 489,472	$ 1,048,238	$ 938,979
Intercompany revenue	0	0	0	0
Total revenue	548,785	489,472	1,048,238	938,979
Direct costs	407,938	369,057	793,529	717,113
Gross profit	140,847	120,415	254,709	221,866
Selling, general and administrative expense	44,485	39,931	88,883	81,371
Operating income (loss) before sale or disposal of assets	96,362	80,484	165,826	140,495
Net loss (gain) on sale or disposal of assets	(819)	578	(484)	(643)
Operating income (loss)	97,181	79,906	166,310	141,138
Depreciation and amortization	20,366	20,030	40,163	39,797
Property and equipment additions	17,995	11,360	34,521	27,979
Total assets	2,397,110		2,397,110		$ 2,332,020
Operating Segments [Member] | Animal Hospital [Member]
Lines of Business
External revenue	435,376	386,776	828,402	738,364
Intercompany revenue	0	0	0	0
Total revenue	435,376	386,776	828,402	738,364
Direct costs	361,991	323,440	699,533	626,228
Gross profit	73,385	63,336	128,869	112,136
Selling, general and administrative expense	10,453	9,864	21,674	18,992
Operating income (loss) before sale or disposal of assets	62,932	53,472	107,195	93,144
Net loss (gain) on sale or disposal of assets	(914)	414	(620)	582
Operating income (loss)	63,846	53,058	107,815	92,562
Depreciation and amortization	16,440	15,110	32,512	29,852
Property and equipment additions	13,995	8,119	26,077	21,187
Total assets	2,092,935		2,092,935		2,021,725
Operating Segments [Member] | Laboratory [Member]
Lines of Business
External revenue	89,707	81,320	168,516	156,103
Intercompany revenue	16,515	14,635	31,678	28,386
Total revenue	106,222	95,955	200,194	184,489
Direct costs	49,519	46,863	95,509	92,366
Gross profit	56,703	49,092	104,685	92,123
Selling, general and administrative expense	9,487	8,281	18,352	16,299
Operating income (loss) before sale or disposal of assets	47,216	40,811	86,333	75,824
Net loss (gain) on sale or disposal of assets	35	(7)	41	(78)
Operating income (loss)	47,181	40,818	86,292	75,902
Depreciation and amortization	2,705	2,563	5,209	5,098
Property and equipment additions	2,862	1,304	6,078	3,285
Total assets	304,685		304,685		258,550
Operating Segments [Member] | All Other [Member]
Lines of Business
External revenue	22,818	20,457	49,351	42,658
Intercompany revenue	5,851	3,255	13,545	9,175
Total revenue	28,669	23,712	62,896	51,833
Direct costs	17,280	16,064	40,083	34,216
Gross profit	11,389	7,648	22,813	17,617
Selling, general and administrative expense	7,741	7,411	16,428	15,759
Operating income (loss) before sale or disposal of assets	3,648	237	6,385	1,858
Net loss (gain) on sale or disposal of assets	11	97	20	(1,087)
Operating income (loss)	3,637	140	6,365	2,945
Depreciation and amortization	1,176	2,004	2,328	4,140
Property and equipment additions	500	920	1,300	1,678
Total assets	80,994		80,994		89,596
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	16,804	14,375	32,429	30,321
Operating income (loss) before sale or disposal of assets	(16,804)	(14,375)	(32,429)	(30,321)
Net loss (gain) on sale or disposal of assets	49	74	75	(60)
Operating income (loss)	(16,853)	(14,449)	(32,504)	(30,261)
Depreciation and amortization	575	826	1,167	1,645
Property and equipment additions	1,512	1,333	2,576	2,744
Total assets	340,002		340,002		270,414
Eliminations [Member]
Lines of Business
External revenue	884	919	1,969	1,854
Intercompany revenue	(22,366)	(17,890)	(45,223)	(37,561)
Total revenue	(21,482)	(16,971)	(43,254)	(35,707)
Direct costs	(20,852)	(17,310)	(41,596)	(35,697)
Gross profit	(630)	339	(1,658)	(10)
Selling, general and administrative expense	0	0	0	0
Operating income (loss) before sale or disposal of assets	(630)	339	(1,658)	(10)
Net loss (gain) on sale or disposal of assets	0	0	0	0
Operating income (loss)	(630)	339	(1,658)	(10)
Depreciation and amortization	(530)	(473)	(1,053)	(938)
Property and equipment additions	(874)	$ (316)	(1,510)	$ (915)
Total assets	$ (421,506)		$ (421,506)		$ (308,265)