Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income	$ 177,311	$ 181,574	$ 136,096
Adjustments to reconcile net income to net cash provided by operating activities:
Bad debt expense	36,950	31,849	23,257
Depreciation and amortization expense	125,504	116,783	118,120
Net loss (gain) on disposal of property and equipment	105	(43)	(58)
Amortization of debt issuance costs	1,846	1,769	1,769
Amortization of discount on bonds payable	19,835	18,495	17,246
Stock-based compensation expense	20,766	25,244	25,516
Deferred income taxes	62,983	51,449	37,745
Excess tax benefit from stock-based compensation	(395)	(802)	(39)
Change in assets and liabilities net of effects of acquired businesses:
Accounts receivable	(94,775)	(58,308)	(5,990)
Inventories	(1,570)	1,038	(4,146)
Prepaid and other assets	(5,949)	179	(807)
Accounts payable	(5,575)	13,157	(627)
Accrued expenses and other current liabilities	(24,508)	(5,663)	1,029
Income taxes payable	4,982	(4,673)	4,013
Long-term obligations	(2,787)	(11,269)	0
Net cash provided by operating activities	314,723	360,779	353,124
Cash flows from investing activities:
Proceeds from sale of property and equipment	343	64	132
Capital expenditures	(130,932)	(110,253)	(110,091)
Purchases of investments	(80,862)	(40,000)	0
Sales and maturities of investments	80,923	58,650	1,750
Cash restricted for future payments	345	(345)	0
Business acquisitions, net of cash acquired	(111,032)	(11,375)	(5,077)
Net cash used in investing activities	(241,215)	(103,259)	(113,286)
Cash flows from financing activities:
Proceeds from revolving credit line	130,000	0	0
Payments on revolving credit line	(30,000)	0	0
Payments of principal on debt and long-term obligations	(10,878)	(2,055)	(4,813)
Payments of debt related costs	(1,847)	(63)	(63)
Proceeds from exercise of stock options and issuance of common shares	14,553	26,768	56,026
Excess tax benefit from stock-based compensation	395	802	39
Payments of cash dividends	(74,920)	(39,236)	0
Payments to acquire treasury stock	(249,986)	(99,961)	(343,250)
Net cash used in financing activities	(222,683)	(113,745)	(292,061)
Net (decrease) increase in cash and cash equivalents	(149,175)	143,775	(52,223)
Cash and cash equivalents, beginning of year	164,203	20,428	72,651
Cash and cash equivalents, end of year	15,028	164,203	20,428
Supplemental disclosure of cash flow information:
Cash paid for interest	15,628	15,125	15,148
Cash paid for income taxes	$ 45,863	$ 71,104	$ 51,069