Condensed, Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Cash flows from operating activities:
Net income	$ 34,915	[1]	$ 31,823	[1]
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	19,767		18,239
Amortization of debt issue costs	304		314
Provision for uncollectible accounts	890		1,093
Net (gain) loss on disposal of assets	(1,221)		1,726
Share-based compensation	4,544		3,770
Deferred income taxes	0		2,868
Excess tax benefit from exercise of stock options	(392)		(62)
Other	(905)		(414)
Changes in operating assets and liabilities:
Trade accounts receivable	(5,825)		(16,126)
Inventory, prepaid expense and other assets	(1,389)		(2,491)
Accounts payable and other accrued liabilities	(3,773)		12,127
Accrued payroll and related liabilities	6,247		9,149
Income taxes	15,165		13,235
Net cash provided by operating activities	68,327		75,251
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(17,295)		(6,756)
Real estate acquired in connection with business acquisitions	0		(510)
Capital expenditures	(16,619)		(17,969)
Proceeds from sale of assets	859		177
Other	520		(115)
Net cash used in investing activities	(32,535)		(25,173)
Cash flows from financing activities:
Repayment of debt	(12,806)		(8,733)
Distributions to noncontrolling interest partners	(1,090)		(1,197)
Purchase of noncontrolling interests	(326)		(5,032)
Proceeds from issuance of common stock under stock option plans	372		1,876
Excess tax benefit from exercise of stock options	392		62
Stock repurchases	(9,793)		(59)
Net cash used in financing activities	(23,251)		(13,083)
Effect of currency exchange rate changes on cash and cash equivalents	(282)		(144)
Increase in cash and cash equivalents	12,259		36,851
Cash and cash equivalents at beginning of period	125,029
Cash and cash equivalents at end of period	137,288		105,286
Supplemental disclosures of cash flow information:
Interest paid	3,708		3,999
Income taxes paid	6,853		3,808
Detail of acquisitions:
Fair value of assets acquired	18,550		6,969
Noncontrolling interest	(855)		0
Cash paid for acquisitions, net of acquired cash	(17,295)		(6,756)
Contingent consideration	0		(53)
Holdbacks	(400)		(160)
Liabilities assumed	$ 0		$ 0

[1] Includes approximately $0.5 million and $0.7 million of net income related to redeemable and mandatorily redeemable noncontrolling interests for the three months ended March 31, 2014 and 2013, respectively.