Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 159,660	$ 166,171	$ 136,142
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on disposal of assets	1,627	1,657	571
Depreciation	169,027	147,036	132,874
Amortization of intangibles	24,557	20,064	14,582
Deferred income taxes, net of acquisitions	29,689	50,989	26,431
Loss on redemption of 2026 Convertible Senior Notes, net of make-whole payment			2,255
Amortization of debt issuance costs	1,993	1,420	1,574
Amortization of debt discount			1,245
Equity-based compensation	17,289	11,879	11,331
Interest income on restricted assets	(603)	(454)	(511)
Interest accretion	4,000	2,771	1,778
Excess tax benefit associated with equity-based compensation	(5,033)	(4,763)	(11,997)
Changes in operating assets and liabilities, net of effects from acquisitions:
Accounts receivable, net	1,549	(14,507)	(9,321)
Prepaid expenses and other current assets	(733)	(4,236)	3,304
Accounts payable	2,761	(2,912)	(853)
Deferred revenue	180	4,161	3,244
Accrued liabilities	7,835	9,551	19,074
Other long-term liabilities	2,529	(657)	456
Net cash provided by operating activities	416,327	388,170	332,179
CASH FLOWS FROM INVESTING ACTIVITIES:
Payments for acquisitions, net of cash acquired	(1,579,869)	(257,852)	(81,010)
Capital expenditures for property and equipment	(153,517)	(141,924)	(134,829)
Proceeds from disposal of assets	2,741	4,434	6,659
Decrease (increase) in restricted assets, net of interest income	2,983	351	(2,552)
Other	(6,185)	(5,014)	(2,492)
Net cash used in investing activities	(1,733,847)	(400,005)	(214,224)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from long-term debt	1,647,000	592,500	483,253
Principal payments on notes payable and long-term debt	(609,014)	(421,872)	(467,660)
Payment of contingent consideration	(12,473)	(500)
Change in book overdraft	398	(227)	279
Proceeds from option and warrant exercises	4,057	5,159	33,074
Excess tax benefit associated with equity-based compensation	5,033	4,763	11,997
Payments for repurchase of common stock	(18,597)	(116,817)	(166,320)
Payments for cash dividends	(44,465)	(35,566)	(8,561)
Tax withholdings related to net share settlements of restricted stock units	(6,062)	(5,511)	(3,783)
Distributions to noncontrolling interests	(198)	(675)
Debt issuance costs	(7,174)	(6,649)
Proceeds from common stock offering, net	369,584
Net cash provided by (used in) financing activities	1,328,089	14,605	(117,721)
Net increase in cash and equivalents	10,569	2,770	234
Cash and equivalents at beginning of year	12,643	9,873	9,639
Cash and equivalents at end of year	23,212	12,643	9,873
SUPPLEMENTARY DISCLOSURES OF CASH FLOW INFORMATION AND NON-CASH TRANSACTIONS:
Cash paid for income taxes	69,954	52,729	50,111
Cash paid for interest	49,826	39,499	39,913
In connection with its acquisitions, the Company assumed liabilities as follows:
Fair value of assets acquired	1,748,458	404,550	107,144
Cash paid for current year acquisitions	(1,579,869)	(257,852)	(81,010)
Liabilities assumed and notes payable issued to sellers of businesses acquired	$ 168,589	$ 146,698	$ 26,134