Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:
Net income	$ 172,407	$ 146,588
Adjustments to reconcile net income to net cash provided by operating activities:
Loss on disposal of assets and impairments	7,535	11,895
Depreciation	171,920	162,277
Amortization of intangibles	20,158	18,861
Deferred income taxes, net of acquisitions	4,572	24,411
Amortization of debt issuance costs	2,362	2,836
Equity-based compensation	13,889	11,268
Interest income on restricted assets	(345)	(295)
Interest accretion	3,631	3,677
Excess tax benefit associated with equity-based compensation	(7,177)	(3,539)
Payment of contingent consideration recorded in earnings		(5,059)
Net change in operating assets and liabilities, net of acquisitions	25,674	12,484
Net cash provided by operating activities	414,626	385,404
Cash flows from investing activities:
Payments for acquisitions, net of cash acquired	(49,231)	(2,031)
Proceeds from adjustment to acquisition consideration	843	18,000
Capital expenditures for property and equipment	(148,843)	(140,872)
Proceeds from disposal of assets	6,139	9,075
Increase in restricted assets, net of interest income	(2,370)	(81)
Other	18	(4,868)
Net cash used in investing activities	(193,444)	(120,777)
Cash flows from financing activities:
Proceeds from long-term debt	214,000	212,500
Principal payments on notes payable and long-term debt	(394,761)	(418,316)
Payment of contingent consideration recorded at acquisition date	(578)	(23,530)
Change in book overdraft	(180)	(374)
Proceeds from option and warrant exercises	2,958	2,234
Excess tax benefit associated with equity-based compensation	7,177	3,539
Payments for cash dividends	(42,770)	(37,005)
Tax withholdings related to net share settlements of restricted stock units	(6,796)	(5,421)
Distributions to noncontrolling interests	(371)	(198)
Debt issuance costs	(125)	(1,987)
Net cash used in financing activities	(221,446)	(268,558)
Net decrease in cash and equivalents	(264)	(3,931)
Cash and equivalents at beginning of period	13,591	23,212
Cash and equivalents at end of period	13,327	19,281
Non-cash financing activity:
Liabilities assumed and notes payable issued to sellers of businesses acquired	$ 5,370	$ 486