Lines of Business (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Lines of Business
External revenue	$ 551,717	$ 499,577	$ 1,599,955	$ 1,438,556
Intercompany revenue	0	0	0	0
Total revenue	551,717	499,577	1,599,955	1,438,556
Direct costs	414,051	375,820	1,207,580	1,092,933
Gross profit	137,666	123,757	392,375	345,623
Selling, general and administrative expense	44,860	42,792	133,743	124,163
Operating income (loss) before sale or disposal of assets	92,806	80,965	258,632	221,460
Impairment of goodwill and other long-lived assets	0	27,019	0	27,019
Business interruption insurance gain	(4,523)	0	(4,523)	0
Net loss (gain) on sale or disposal of assets	250	470	(234)	(173)
Operating income (loss)	97,079	53,476	263,389	194,614
Depreciation and amortization	20,471	19,862	60,634	59,659
Property and equipment additions	26,949	22,114	61,470	50,093
Total assets	2,431,190		2,431,190		$ 2,332,020
Operating Segments [Member] | Animal Hospital [Member]
Lines of Business
External revenue	441,924	395,820	1,270,326	1,134,184
Intercompany revenue	0	0	0	0
Total revenue	441,924	395,820	1,270,326	1,134,184
Direct costs	366,983	327,283	1,066,516	953,511
Gross profit	74,941	68,537	203,810	180,673
Selling, general and administrative expense	10,677	9,269	32,351	28,261
Operating income (loss) before sale or disposal of assets	64,264	59,268	171,459	152,412
Impairment of goodwill and other long-lived assets		0		0
Business interruption insurance gain	0		0
Net loss (gain) on sale or disposal of assets	175	598	(445)	1,180
Operating income (loss)	64,089	58,670	171,904	151,232
Depreciation and amortization	16,520	15,201	49,032	45,053
Property and equipment additions	19,429	17,224	45,506	38,411
Total assets	2,147,136		2,147,136		2,021,725
Operating Segments [Member] | Laboratory [Member]
Lines of Business
External revenue	84,129	77,394	252,645	233,497
Intercompany revenue	16,180	14,509	47,858	42,895
Total revenue	100,309	91,903	300,503	276,392
Direct costs	48,901	46,879	144,410	139,245
Gross profit	51,408	45,024	156,093	137,147
Selling, general and administrative expense	9,542	8,610	27,894	24,909
Operating income (loss) before sale or disposal of assets	41,866	36,414	128,199	112,238
Impairment of goodwill and other long-lived assets		0		0
Business interruption insurance gain	0		0
Net loss (gain) on sale or disposal of assets	0	7	41	(71)
Operating income (loss)	41,866	36,407	128,158	112,309
Depreciation and amortization	2,731	2,671	7,940	7,769
Property and equipment additions	5,735	2,391	11,813	5,676
Total assets	304,807		304,807		258,550
Operating Segments [Member] | All Other [Member]
Lines of Business
External revenue	24,544	25,397	73,895	68,055
Intercompany revenue	6,294	4,684	19,839	13,859
Total revenue	30,838	30,081	93,734	81,914
Direct costs	19,077	19,945	59,160	54,161
Gross profit	11,761	10,136	34,574	27,753
Selling, general and administrative expense	7,660	8,023	24,088	23,782
Operating income (loss) before sale or disposal of assets	4,101	2,113	10,486	3,971
Impairment of goodwill and other long-lived assets		27,019		27,019
Business interruption insurance gain	(4,523)		(4,523)
Net loss (gain) on sale or disposal of assets	72	0	92	(1,087)
Operating income (loss)	8,552	(24,906)	14,917	(21,961)
Depreciation and amortization	1,181	1,781	3,509	5,921
Property and equipment additions	127	1,123	1,427	2,801
Total assets	76,969		76,969		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	16,981	16,890	49,410	47,211
Operating income (loss) before sale or disposal of assets	(16,981)	(16,890)	(49,410)	(47,211)
Impairment of goodwill and other long-lived assets		0		0
Business interruption insurance gain	0		0
Net loss (gain) on sale or disposal of assets	3	(135)	78	(195)
Operating income (loss)	(16,984)	(16,755)	(49,488)	(47,016)
Depreciation and amortization	588	688	1,755	2,333
Property and equipment additions	2,773	2,025	5,349	4,769
Total assets	391,471		391,471		270,414
Eliminations [Member]
Lines of Business
External revenue	1,120	966	3,089	2,820
Intercompany revenue	(22,474)	(19,193)	(67,697)	(56,754)
Total revenue	(21,354)	(18,227)	(64,608)	(53,934)
Direct costs	(20,910)	(18,287)	(62,506)	(53,984)
Gross profit	(444)	60	(2,102)	50
Selling, general and administrative expense	0	0	0	0
Operating income (loss) before sale or disposal of assets	(444)	60	(2,102)	50
Impairment of goodwill and other long-lived assets		0		0
Business interruption insurance gain	0		0
Net loss (gain) on sale or disposal of assets	0	0	0	0
Operating income (loss)	(444)	60	(2,102)	50
Depreciation and amortization	(549)	(479)	(1,602)	(1,417)
Property and equipment additions	(1,115)	$ (649)	(2,625)	$ (1,564)
Total assets	$ (489,193)		$ (489,193)		$ (308,265)