Condensed, Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 41,911	$ 35,642	$ 117,194	$ 107,741
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			57,783	56,882
Amortization of debt issue costs			937	961
Provision for uncollectible accounts			5,380	4,437
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	0	0	0	(5,719)
Net (gain) loss on sale of assets	(109)	387	1,187	1,022
Share-based compensation			10,340	10,466
Deferred income taxes			2,868	14,119
Excess tax benefit from exercise of stock options			(2,654)	(358)
Other			(251)	(838)
Changes in operating assets and liabilities:
Trade accounts receivable			(9,986)	(5,079)
Inventory, prepaid expense and other assets			(1,634)	(6,727)
Accounts payable and other accrued liabilities			4,941	3,161
Accrued payroll and related liabilities			11,408	10,007
Income taxes			21,492	(1,636)
Net cash provided by operating activities			219,005	188,439
Cash flows from investing activities:
Business acquisitions, net of cash acquired			(39,640)	(108,031)
Real estate acquired in connection with business acquisitions	(1,200)		(1,208)	(1,602)
Property and equipment additions			(52,682)	(55,257)
Proceeds from sale of assets			905	112
Other			(1,738)	(1,583)
Net cash used in investing activities			(94,363)	(166,361)
Cash flows from financing activities:
Repayment of debt			(28,507)	(52,040)
Proceeds from issuance of long-term debt			0	50,000
Proceeds from revolving credit facility			0	50,000
Repayment of revolving credit facility			0	(50,000)
Payment of financing costs			0	(122)
Payments of Ordinary Dividends, Noncontrolling Interest			3,324	2,802
Payments to Acquire Additional Interest in Subsidiaries			(5,727)	0
Proceeds from issuance of common stock under stock option plans			15,111	3,322
Excess tax benefit from exercise of stock options			2,654	358
Payments for Repurchase of Common Stock			(19,384)	(3,897)
Other			(160)	(1,273)
Net cash provided by (used in) financing activities			(39,337)	(6,454)
Effect of currency exchange rate changes on cash and cash equivalents			(566)	386
Decrease in cash and cash equivalents			84,739	16,010
Cash and cash equivalents at beginning of period			68,435	63,651
Cash and cash equivalents at end of period	153,174	79,661	153,174	79,661
Supplemental disclosures of cash flow information:
Interest paid	9,487	11,614
Income taxes paid	47,305	48,671
Detail of acquisitions:
Fair value of assets acquired		187,515	58,825
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value	0	(11,850)	0	(11,850)
Noncontrolling Interest, Increase from Business Combination		8,161	(5,406)	8,161
Cash paid for acquisitions	(39,640)	(108,031)	(39,640)	(108,031)
CashPaidToDebtHolders		(25,915)	(2,360)
Stock Issued During Period, Value, Acquisitions	0	(10,500)		(10,500)
Contingent consideration	(1,120)	(934)	(1,120)	(934)
Holdbacks	(892)	(2,525)
Liabilities assumed	9,407	19,599
Capital Lease Obligations Incurred			$ 21,668	$ 0