Lines of Business (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Lines of Business
External revenue	$ 499,577	$ 464,055	$ 1,438,556	$ 1,367,916
Intercompany revenue	0	0	0	0
Total revenue	499,577	464,055	1,438,556	1,367,916
Direct costs	375,820	353,378	1,092,933	1,046,022
Gross profit	123,757	110,677	345,623	321,894
Selling, general and administrative expense	42,792	38,747	124,163	117,616
Operating income (loss) before charges	80,965	71,930	221,460	204,278
Impairment of goodwill and other long-lived assets	27,019	0	27,019	0
Net (gain) loss on sale or disposal of assets	470	(109)	(173)	1,187
Operating income (loss)	53,476	72,039	194,614	203,091
Depreciation and amortization	19,862	20,044	59,659	57,783
Capital expenditures	22,114	19,587	50,093	52,682
Total assets	2,272,485		2,272,485		2,237,781
Operating Segments [Member] | Animal Hospital [Member]
Lines of Business
External revenue	395,820	368,868	1,134,184	1,074,688
Intercompany revenue	0	0	0	0
Total revenue	395,820	368,868	1,134,184	1,074,688
Direct costs	327,283	308,029	953,511	908,537
Gross profit	68,537	60,839	180,673	166,151
Selling, general and administrative expense	9,269	8,678	28,261	25,723
Operating income (loss) before charges	59,268	52,161	152,412	140,428
Impairment of goodwill and other long-lived assets	0
Net (gain) loss on sale or disposal of assets	598	(110)	1,180	1,459
Operating income (loss)	58,670	52,271	151,232	138,969
Depreciation and amortization	15,201	15,037	45,053	43,108
Capital expenditures	17,224	15,915	38,411	41,682
Total assets	1,904,183		1,904,183		1,854,609
Operating Segments [Member] | Laboratory [Member]
Lines of Business
External revenue	77,394	72,877	233,497	223,466
Intercompany revenue	14,509	13,583	42,895	41,559
Total revenue	91,903	86,460	276,392	265,025
Direct costs	46,879	45,650	139,245	136,524
Gross profit	45,024	40,810	137,147	128,501
Selling, general and administrative expense	8,610	7,921	24,909	23,891
Operating income (loss) before charges	36,414	32,889	112,238	104,610
Impairment of goodwill and other long-lived assets	0		0
Net (gain) loss on sale or disposal of assets	7	11	(71)	5
Operating income (loss)	36,407	32,878	112,309	104,605
Depreciation and amortization	2,671	2,554	7,769	7,651
Capital expenditures	2,391	1,905	5,676	5,641
Total assets	261,245		261,245		247,591
Operating Segments [Member] | All Other [Member]
Lines of Business
External revenue	25,397	21,482	68,055	67,339
Intercompany revenue	4,684	5,980	13,859	16,118
Total revenue	30,081	27,462	81,914	83,457
Direct costs	19,945	17,456	54,161	54,394
Gross profit	10,136	10,006	27,753	29,063
Selling, general and administrative expense	8,023	7,618	23,782	24,573
Operating income (loss) before charges	2,113	2,388	3,971	4,490
Impairment of goodwill and other long-lived assets	27,019		27,019
Net (gain) loss on sale or disposal of assets	0	0	(1,087)	3
Operating income (loss)	(24,906)	2,388	(21,961)	4,487
Depreciation and amortization	1,781	2,087	5,921	5,989
Capital expenditures	1,123	872	2,801	3,244
Total assets	85,031		85,031		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	16,890	14,530	47,211	43,429
Operating income (loss) before charges	(16,890)	(14,530)	(47,211)	(43,429)
Impairment of goodwill and other long-lived assets	0		0
Net (gain) loss on sale or disposal of assets	(135)	(10)	(195)	(280)
Operating income (loss)	(16,755)	(14,520)	(47,016)	(43,149)
Depreciation and amortization	688	816	2,333	2,370
Capital expenditures	2,025	1,795	4,769	3,741
Total assets	174,308		174,308		77,153
Eliminations [Member]
Lines of Business
External revenue	966	828	2,820	2,423
Intercompany revenue	(19,193)	(19,563)	(56,754)	(57,677)
Total revenue	(18,227)	(18,735)	(53,934)	(55,254)
Direct costs	(18,287)	(17,757)	(53,984)	(53,433)
Gross profit	60	(978)	50	(1,821)
Selling, general and administrative expense	0	0	0	0
Operating income (loss) before charges	60	(978)	50	(1,821)
Impairment of goodwill and other long-lived assets	0		0
Net (gain) loss on sale or disposal of assets	0	0	0	0
Operating income (loss)	60	(978)	50	(1,821)
Depreciation and amortization	(479)	(450)	(1,417)	(1,335)
Capital expenditures	(649)	(900)	(1,564)	(1,626)
Total assets	$ (152,282)		$ (152,282)		$ (37,817)