Lines of Business (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Lines of Business
External revenue	$ 653,489	$ 548,785	$ 1,216,928	$ 1,048,238
Intercompany revenue	0	0	0	0
Total revenue	653,489	548,785	1,216,928	1,048,238
Direct costs	489,541	407,938	916,200	793,529
Gross profit	163,948	140,847	300,728	254,709
Selling, general and administrative expense	48,190	44,485	98,318	88,883
Operating income (loss) before sale or disposal of assets	115,758	96,362	202,410	165,826
Net (gain) loss on sale or disposal of assets	(271)	(819)	292	(484)
Operating income (loss)	116,029	97,181	202,118	166,310
Depreciation and amortization	25,689	20,366	46,978	40,163
Property and equipment additions	33,008	17,995	58,814	34,521
Total assets	3,179,127		3,179,127		$ 2,501,132
Operating Segments | Animal Hospital
Lines of Business
External revenue	540,376	435,376	998,999	828,402
Intercompany revenue	0	0	0	0
Total revenue	540,376	435,376	998,999	828,402
Direct costs	445,697	361,991	830,903	699,533
Gross profit	94,679	73,385	168,096	128,869
Selling, general and administrative expense	14,277	10,453	26,362	21,674
Operating income (loss) before sale or disposal of assets	80,402	62,932	141,734	107,195
Net (gain) loss on sale or disposal of assets	(132)	(914)	443	(620)
Operating income (loss)	80,534	63,846	141,291	107,815
Depreciation and amortization	21,875	16,440	39,448	32,512
Property and equipment additions	25,486	13,995	44,030	26,077
Total assets	2,888,883		2,888,883		2,186,959
Operating Segments | Laboratory
Lines of Business
External revenue	93,265	89,707	182,505	168,516
Intercompany revenue	18,795	16,515	36,282	31,678
Total revenue	112,060	106,222	218,787	200,194
Direct costs	51,513	49,519	101,524	95,509
Gross profit	60,547	56,703	117,263	104,685
Selling, general and administrative expense	9,702	9,487	19,998	18,352
Operating income (loss) before sale or disposal of assets	50,845	47,216	97,265	86,333
Net (gain) loss on sale or disposal of assets	(35)	35	(35)	41
Operating income (loss)	50,880	47,181	97,300	86,292
Depreciation and amortization	2,839	2,705	5,620	5,209
Property and equipment additions	4,750	2,862	9,402	6,078
Total assets	326,719		326,719		306,296
Operating Segments | All Other
Lines of Business
External revenue	18,656	22,818	33,110	49,351
Intercompany revenue	4,741	5,851	9,700	13,545
Total revenue	23,397	28,669	42,810	62,896
Direct costs	14,480	17,280	26,983	40,083
Gross profit	8,917	11,389	15,827	22,813
Selling, general and administrative expense	6,022	7,741	11,321	16,428
Operating income (loss) before sale or disposal of assets	2,895	3,648	4,506	6,385
Net (gain) loss on sale or disposal of assets	3	11	3	20
Operating income (loss)	2,892	3,637	4,503	6,365
Depreciation and amortization	904	1,176	1,787	2,328
Property and equipment additions	1,485	500	2,092	1,300
Total assets	68,336		68,336		73,491
Corporate, Non-Segment
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	18,189	16,804	40,637	32,429
Operating income (loss) before sale or disposal of assets	(18,189)	(16,804)	(40,637)	(32,429)
Net (gain) loss on sale or disposal of assets	(107)	49	(119)	75
Operating income (loss)	(18,082)	(16,853)	(40,518)	(32,504)
Depreciation and amortization	668	575	1,306	1,167
Property and equipment additions	2,336	1,512	5,187	2,576
Total assets	1,338,562		1,338,562		471,112
Eliminations
Lines of Business
External revenue	1,192	884	2,314	1,969
Intercompany revenue	(23,536)	(22,366)	(45,982)	(45,223)
Total revenue	(22,344)	(21,482)	(43,668)	(43,254)
Direct costs	(22,149)	(20,852)	(43,210)	(41,596)
Gross profit	(195)	(630)	(458)	(1,658)
Selling, general and administrative expense	0	0	0	0
Operating income (loss) before sale or disposal of assets	(195)	(630)	(458)	(1,658)
Net (gain) loss on sale or disposal of assets	0	0	0	0
Operating income (loss)	(195)	(630)	(458)	(1,658)
Depreciation and amortization	(597)	(530)	(1,183)	(1,053)
Property and equipment additions	(1,049)	$ (874)	(1,897)	$ (1,510)
Total assets	$ (1,443,373)		$ (1,443,373)		$ (536,726)