Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 216,098	$ 140,683	$ 142,922
Adjustments to reconcile net income to net cash provided by operating activities:
Impairment of goodwill and other long-lived assets	0	27,019	0
Gain on sale of business	(43,306)	0	0
Depreciation and amortization	81,688	79,427	77,409
Amortization of debt issue costs	1,741	1,391	1,245
Provision for uncollectible accounts	8,401	6,248	7,360
Debt retirement costs	0	1,709	0
Net loss (gain) on sale or disposal of assets	829	(1,152)	2,455
Share-based compensation	16,264	17,200	14,104
Deferred income taxes	56,722	8,853	18,064
Excess tax benefits from stock based compensation	(11,089)	(6,241)	(3,446)
Other	2,159	531	(377)
Changes in operating assets and liabilities:
Trade accounts receivable	(28,720)	(3,900)	(11,048)
Inventory, prepaid expenses and other assets	(9,716)	(22,897)	(7,134)
Accounts payable and other accrued liabilities	10,812	11,597	557
Accrued payroll and related liabilities	11,323	6,782	6,502
Income taxes	4,339	2,960	7,759
Net cash provided by operating activities	317,545	270,210	256,372
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(151,586)	(147,507)	(58,016)
Investment in Vetstreet Inc.	(9,552)	0	0
Property and equipment additions	(95,234)	(72,948)	(73,270)
Proceeds from sale or disposal of assets	6,762	3,904	7,096
Proceeds from sale of business	48,000	0	0
Other	(2,042)	(2,691)	(2,541)
Net cash used in investing activities	(203,652)	(219,242)	(126,731)
Cash flows from financing activities:
Repayment of long-term obligations	(35,017)	(568,011)	(41,129)
Proceeds from the issuance of long-term obligations	0	600,000	0
Payment of financing costs	97,000	135,000	0
Payments of Financing Costs	0	(7,987)	0
Distributions to noncontrolling interest partners	(4,962)	(5,009)	(4,866)
Purchase of noncontrolling interests	(2,500)	(326)	(6,581)
Proceeds from issuance of common stock under stock incentive plans	2,683	2,859	17,233
Excess tax benefits from stock based compensation	11,089	6,241	3,446
Stock repurchases	(165,607)	(255,108)	(39,367)
Other	2,041	(1,424)	(749)
Net cash used in financing activities	(95,273)	(93,765)	(72,013)
Effect of currency exchange rate changes on cash and cash equivalents	(1,115)	(849)	(1,034)
Increase (decrease) in cash and cash equivalents	17,505	(43,646)	56,594
Cash and cash equivalents at beginning of year	81,383	125,029	68,435
Cash and cash equivalents at end of year	98,888	81,383	125,029
Supplemental disclosures of cash flow information:
Interest paid	18,517	15,049	16,422
Income taxes paid	74,315	75,098	61,825
Supplemental schedule of non-cash investing and financing activities:
Capital lease additions	0	$ 0	$ 21,668
Vetstreet [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale of business	(43,300)
Detail of Vetstreet sale:
Accounts receivable, net	(4,480)
Prepaid and other	(1,300)
Fixed assets, net	(487)
Intangibles	(2,567)
Liabilities	4,140
Total Assets and Liabilities	$ (4,694)