CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash flows from operating activities:
Net income	$ 123,574	$ 127,983
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on disposal of assets	715	742
Depreciation	119,331	108,843
Amortization of intangibles	18,115	14,788
Deferred income taxes, net of acquisitions	18,451	36,960
Amortization of debt issuance costs	1,247	1,005
Equity-based compensation	14,036	8,906
Interest income on restricted assets	(491)	(355)
Interest accretion	2,798	1,977
Excess tax benefit associated with equity-based compensation	(3,415)	(4,500)
Net change in operating assets and liabilities, net of acquisitions	32,378	1,375
Net cash provided by operating activities	326,739	297,724
Cash flows from investing activities:
Payments for acquisitions, net of cash acquired	(223,256)	(247,862)
Capital expenditures for property and equipment	(110,995)	(84,051)
Proceeds from disposal of assets	2,107	3,238
Decrease in restricted assets, net of interest income	4,779	2,241
Other	(6,287)	(1,706)
Net cash used in investing activities	(333,652)	(328,140)
Cash flows from financing activities:
Proceeds from long-term debt	334,000	515,500
Principal payments on notes payable and long-term debt	(545,069)	(343,726)
Payment of contingent consideration	(4,099)	(100)
Change in book overdraft	(3,383)	(937)
Proceeds from option and warrant exercises	1,042	4,956
Excess tax benefit associated with equity-based compensation	3,415	4,500
Payments for repurchase of common stock	(18,597)	(85,068)
Payments for cash dividends	(32,182)	(25,497)
Tax withholdings related to net share settlements of restricted stock units	(6,039)	(5,436)
Distributions to noncontrolling interests	(94)	(675)
Debt issuance costs	(776)	(6,414)
Proceeds from common stock offering, net	369,584
Net cash provided by financing activities	97,802	57,103
Net increase in cash and equivalents	90,889	26,687
Cash and equivalents at beginning of period	12,643	9,873
Cash and equivalents at end of period	103,532	36,560
Non-cash financing activity:
Liabilities assumed and notes payable issued to sellers of businesses acquired	$ 51,004	$ 144,386