Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Cash flows from operating activities:
Net income	$ 89,142	$ 90,051
Adjustments to reconcile net income to net cash provided by operating activities:
Bad debt expense	17,612	12,426
Depreciation and amortization expense	59,304	58,923
Net loss (gain) on disposal of property and equipment	25	(20)
Amortization of debt issuance costs	884	884
Amortization of discount on bonds payable	9,744	9,086
Stock-based compensation expense	10,970	13,274
Deferred income taxes	24,822	13,561
Excess tax benefit from stock-based compensation	(240)	(394)
Change in assets and liabilities net of effects of acquired businesses:
Accounts receivable	(57,023)	(56,767)
Inventories	687	4,462
Prepaid and other assets	(3,972)	298
Accounts payable	(3,454)	1,412
Accrued expenses and other current liabilities	(21,616)	(4,371)
Income taxes payable	7,052	1,371
Long-term obligations	(2,161)	(2,235)
Net cash provided by operating activities	131,776	141,961
Cash flows from investing activities:
Proceeds from sale of property and equipment	125	37
Capital expenditures	(57,823)	(54,947)
Purchases of investments	(40,000)	0
Sales and maturities of investments	40,000	24,950
Business acquisitions, net of cash acquired	(73,021)	(11,327)
Cash restricted for future payments	345	(5,345)
Net cash used in investing activities	(130,374)	(46,632)
Cash flows from financing activities:
Payments of principal on debt	(619)	(569)
Payments of cash dividends	(38,186)	0
Proceeds from exercise of stock options and issuance of common shares	5,104	25,817
Excess tax benefit from stock-based compensation	240	394
Payments to acquire treasury stock	(49,998)	(49,961)
Net cash used in financing activities	(83,459)	(24,319)
Net (decrease) increase in cash and cash equivalents	(82,057)	71,010
Cash and cash equivalents, beginning of period	164,203	20,428
Cash and cash equivalents, end of period	82,146	91,438
Supplemental disclosure of cash flow information:
Cash paid for interest	7,563	7,563
Cash paid for income taxes	$ 25,566	$ 43,709