Lines of Business (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Lines of Business
External revenue	$ 656,854	$ 551,717	$ 1,873,782	$ 1,599,955
Intercompany revenue	0	0	0	0
Total revenue	656,854	551,717	1,873,782	1,599,955
Direct costs	500,277	414,051	1,416,477	1,207,580
Gross profit	156,577	137,666	457,305	392,375
Selling, general and administrative expense	49,343	44,860	147,661	133,743
Operating income (loss) before sale or disposal of assets	107,234	92,806	309,644	258,632
Business interruption insurance gain	0	(4,523)	0	(4,523)
Net loss (gain) on sale or disposal of assets	236	250	528	(234)
Operating income (loss)	106,998	97,079	309,116	263,389
Depreciation and amortization	27,094	20,471	74,072	60,634
Property and equipment additions	31,732	26,949	90,546	61,470
Total assets	3,209,062		3,209,062		$ 2,501,132
Operating Segments | Animal Hospital
Lines of Business
External revenue	553,378	441,924	1,552,377	1,270,326
Intercompany revenue	0	0	0	0
Total revenue	553,378	441,924	1,552,377	1,270,326
Direct costs	459,242	366,983	1,290,145	1,066,516
Gross profit	94,136	74,941	262,232	203,810
Selling, general and administrative expense	15,541	10,677	41,903	32,351
Operating income (loss) before sale or disposal of assets	78,595	64,264	220,329	171,459
Business interruption insurance gain		0
Net loss (gain) on sale or disposal of assets	304	175	747	(445)
Operating income (loss)	78,291	64,089	219,582	171,904
Depreciation and amortization	23,363	16,520	62,811	49,032
Property and equipment additions	24,917	19,429	68,947	45,506
Total assets	2,961,074		2,961,074		2,186,959
Operating Segments | Laboratory
Lines of Business
External revenue	84,970	84,129	267,475	252,645
Intercompany revenue	20,170	16,180	56,452	47,858
Total revenue	105,140	100,309	323,927	300,503
Direct costs	50,934	48,901	152,458	144,410
Gross profit	54,206	51,408	171,469	156,093
Selling, general and administrative expense	9,728	9,542	29,726	27,894
Operating income (loss) before sale or disposal of assets	44,478	41,866	141,743	128,199
Business interruption insurance gain		0
Net loss (gain) on sale or disposal of assets	1	0	(34)	41
Operating income (loss)	44,477	41,866	141,777	128,158
Depreciation and amortization	2,826	2,731	8,446	7,940
Property and equipment additions	4,953	5,735	14,355	11,813
Total assets	329,694		329,694		306,296
Operating Segments | All Other
Lines of Business
External revenue	17,450	24,544	50,560	73,895
Intercompany revenue	5,537	6,294	15,237	19,839
Total revenue	22,987	30,838	65,797	93,734
Direct costs	14,066	19,077	41,049	59,160
Gross profit	8,921	11,761	24,748	34,574
Selling, general and administrative expense	6,064	7,660	17,385	24,088
Operating income (loss) before sale or disposal of assets	2,857	4,101	7,363	10,486
Business interruption insurance gain		(4,523)		(4,523)
Net loss (gain) on sale or disposal of assets	1	72	4	92
Operating income (loss)	2,856	8,552	7,359	14,917
Depreciation and amortization	848	1,181	2,635	3,509
Property and equipment additions	383	127	2,475	1,427
Total assets	70,923		70,923		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	18,010	16,981	58,647	49,410
Operating income (loss) before sale or disposal of assets	(18,010)	(16,981)	(58,647)	(49,410)
Business interruption insurance gain		0
Net loss (gain) on sale or disposal of assets	(70)	3	(189)	78
Operating income (loss)	(17,940)	(16,984)	(58,458)	(49,488)
Depreciation and amortization	679	588	1,985	1,755
Property and equipment additions	2,794	2,773	7,981	5,349
Total assets	1,349,186		1,349,186		471,112
Eliminations
Lines of Business
External revenue	1,056	1,120	3,370	3,089
Intercompany revenue	(25,707)	(22,474)	(71,689)	(67,697)
Total revenue	(24,651)	(21,354)	(68,319)	(64,608)
Direct costs	(23,965)	(20,910)	(67,175)	(62,506)
Gross profit	(686)	(444)	(1,144)	(2,102)
Selling, general and administrative expense	0	0	0	0
Operating income (loss) before sale or disposal of assets	(686)	(444)	(1,144)	(2,102)
Business interruption insurance gain		0
Net loss (gain) on sale or disposal of assets	0	0	0	0
Operating income (loss)	(686)	(444)	(1,144)	(2,102)
Depreciation and amortization	(622)	(549)	(1,805)	(1,602)
Property and equipment additions	(1,315)	$ (1,115)	(3,212)	$ (2,625)
Total assets	$ (1,501,815)		$ (1,501,815)		$ (536,726)