Condensed, Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities:
Net income	$ 31,823	$ 36,321
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	18,239	16,562
Amortization of debt issue costs	314	322
Provision for uncollectible accounts	1,093	1,146
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	0	(5,719)
Net (gain) loss on sale of assets	1,726	523
Share-based compensation	3,770	4,183
Deferred income taxes	2,868	4,212
Excess tax benefit from exercise of stock options	(62)	(187)
Other	(414)	(391)
Changes in operating assets and liabilities:
Trade accounts receivable	(16,126)	(4,606)
Inventory, prepaid expense and other assets	(2,491)	(2,939)
Accounts payable and other accrued liabilities	12,127	814
Accrued payroll and related liabilities	9,149	10,725
Income taxes	13,235	12,698
Net cash provided by operating activities	75,251	73,664
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(6,756)	(65,472)
Real estate acquired in connection with business acquisitions	(510)	0
Property and equipment additions	(17,969)	(16,072)
Proceeds from sale of assets	177	36
Other	(115)	193
Net cash used in investing activities	(25,173)	(81,315)
Cash flows from financing activities:
Repayment of debt	(8,733)	(34,626)
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	(101)
Distributions to noncontrolling interest partners	(1,197)	(719)
Payments to Acquire Additional Interest in Subsidiaries	(5,032)	0
Proceeds from issuance of common stock under stock option plans	1,876	2,621
Excess tax benefit from exercise of stock options	62	187
Stock repurchases	(59)	(579)
Other	0	(151)
Net cash provided by (used in) financing activities	(13,083)	16,632
Effect of currency exchange rate changes on cash and cash equivalents	(144)	84
Decrease in cash and cash equivalents	36,851	9,065
Cash and cash equivalents at beginning of period	68,435	63,651
Cash and cash equivalents at end of period	105,286	72,716
Supplemental disclosures of cash flow information:
Interest paid	3,999	3,854
Income taxes paid	3,808	1,877
Detail of acquisitions:
Fair value of assets acquired	6,969	136,579
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value	0	(11,850)
Noncontrolling Interest, Increase from Business Combination	0	(6,071)
Cash paid for acquisitions	(6,756)	(65,273)
CashPaidToDebtHolders	0	(25,915)
Stock Issued During Period, Value, Acquisitions	0	(10,500)
Contingent consideration	(53)	0
Holdbacks	(160)	(1,275)
Liabilities assumed	$ 0	$ 15,695