Condensed, Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities:
Net income	$ 43,460	$ 35,778	$ 75,283	$ 72,099
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			37,739	37,363
Amortization of debt issue costs			626	642
Provision for uncollectible accounts			3,364	2,551
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	0	0	0	(5,719)
Net (gain) loss on sale of assets	(430)	112	1,296	635
Share-based compensation			7,419	7,767
Deferred income taxes			2,868	10,020
Excess tax benefit from exercise of stock options			(771)	(248)
Other			(384)	(528)
Changes in operating assets and liabilities:
Trade accounts receivable			(17,709)	(6,900)
Inventory, prepaid expense and other assets			(470)	(5,795)
Accounts payable and other accrued liabilities			4,329	(1,805)
Accrued payroll and related liabilities			1,886	1,102
Income taxes			12,595	(2,516)
Net cash provided by operating activities			128,071	108,668
Cash flows from investing activities:
Business acquisitions, net of cash acquired			(21,835)	(75,828)
Real estate acquired in connection with business acquisitions			(510)	0
Property and equipment additions			(33,095)	(37,165)
Proceeds from sale of assets			595	78
Other			(1,042)	55
Net cash used in investing activities			(55,887)	(112,860)
Cash flows from financing activities:
Repayment of debt			(17,442)	(43,318)
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			2,234	1,631
Payments to Acquire Additional Interest in Subsidiaries			(5,030)	0
Proceeds from issuance of common stock under stock option plans			4,181	2,885
Excess tax benefit from exercise of stock options			771	248
Payments for Repurchase of Common Stock			(7,956)	(2,770)
Other			(99)	(656)
Net cash provided by (used in) financing activities			(27,809)	4,636
Effect of currency exchange rate changes on cash and cash equivalents			(540)	(28)
Decrease in cash and cash equivalents			43,835	416
Cash and cash equivalents at beginning of period			68,435	63,651
Cash and cash equivalents at end of period	112,270	64,067	112,270	64,067
Supplemental disclosures of cash flow information:
Interest paid	8,145	7,788
Income taxes paid	30,082	32,685
Detail of acquisitions:
Fair value of assets acquired		147,527	26,473
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value	0	(11,850)	0	(11,850)
Redeemable Noncontrolling Interest Added Through Acquisitions			(3,600)
Noncontrolling Interest, Increase from Business Combination		8,161		8,161
Cash paid for acquisitions	(21,835)	(75,328)	(21,835)	(75,328)
CashPaidToDebtHolders		(25,915)	0
Stock Issued During Period, Value, Acquisitions	0	(10,500)		(10,500)
Contingent consideration	(46)	0	(46)	0
Holdbacks	(460)	(1,525)
Liabilities assumed	532	14,248
Capital Lease Obligations Incurred			$ 21,668	$ 0