Condensed, Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Cash flows from operating activities:
Net income	$ 36,321	$ 30,496
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	16,562	13,380
Amortization of debt issue costs	322	388
Provision for uncollectible accounts	1,146	1,297
Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain	(5,719)	0
Net (gain) loss on sale of assets	523	89
Share-based compensation	4,183	1,068
Deferred income taxes	4,212	8,035
Excess tax benefit from exercise of stock options	(187)	(185)
Other	(391)	(358)
Changes in operating assets and liabilities:
Trade accounts receivable	(4,606)	(6,933)
Inventory, prepaid expense and other assets	(2,939)	1,417
Accounts payable and other accrued liabilities	814	(8,120)
Accrued payroll and related liabilities	10,725	10,734
Income taxes	12,698	9,922
Net cash provided by operating activities	73,664	61,230
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(65,472)	(5,812)
Real estate acquired in connection with business acquisitions	0	(1,200)
Property and equipment additions	(16,072)	(12,034)
Proceeds from sale of assets	36	22
Other	193	(131)
Net cash used in investing activities	(81,315)	(19,155)
Cash flows from financing activities:
Repayment of debt	(34,626)	(7,301)
Proceeds from issuance of long-term debt	50,000	0
Proceeds from revolving credit facility	50,000	0
Repayment of revolving credit facility	(50,000)	0
Payment of financing costs	(101)	0
Distributions to noncontrolling interest partners	(719)	(652)
Proceeds from issuance of common stock under stock option plans	2,621	1,175
Excess tax benefit from exercise of stock options	187	185
Stock repurchases	(579)	(2,337)
Other	(151)	0
Net cash provided by (used in) financing activities	16,632	(8,930)
Effect of currency exchange rate changes on cash and cash equivalents	84	128
Decrease in cash and cash equivalents	9,065	33,273
Cash and cash equivalents at beginning of period	63,651	97,126
Cash and cash equivalents at end of period	72,716	130,399
Supplemental disclosures of cash flow information:
Interest paid	3,854	3,778
Income taxes paid	1,877	976
Detail of acquisitions:
Fair value of assets acquired	136,579	5,350
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value	(11,850)	0
Noncontrolling Interest, Increase from Business Combination	(6,071)	0
Cash paid for acquisitions	(65,273)	(5,150)
CashPaidToDebtHolders	(25,915)	0
Stock Issued During Period, Value, Acquisitions	(10,500)	0
Holdbacks	(1,275)	(200)
Liabilities assumed	$ 15,695	$ 0