Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Cash flows from operating activities:
Net income	$ 112,122	$ 85,674
Adjustments to reconcile net income to net cash provided by operating activities:
Loss (gain) on disposal of assets	(1,465)	3,122
Depreciation	112,922	106,414
Amortization of intangibles	13,456	12,650
Deferred income taxes, net of acquisitions	7,114	14,990
Amortization of debt issuance costs	1,594	2,016
Equity-based compensation	9,444	7,446
Interest income on restricted assets	(235)	(196)
Interest accretion	2,427	2,533
Excess tax benefit associated with equity-based compensation	(7,096)	(2,667)
Loss on prior corporate office lease		10,498
Changes in operating assets and liabilities, net of effects from acquisitions:
Net change in operating assets and liabilities, net of acquisitions	29,398	13,043
Net cash provided by operating activities	279,681	255,523
Cash flows from investing activities:
Payments for acquisitions, net of cash acquired	(29,596)	(1,181)
Proceeds from adjustment to acquisition consideration	843	18,000
Capital expenditures for property and equipment	(83,679)	(87,541)
Proceeds from disposal of assets	5,863	3,622
Increase in restricted assets, net of interest income	(2,015)	(81)
Other	589	(1,140)
Net cash used in investing activities	(107,995)	(68,321)
Cash flows from financing activities:
Proceeds from long-term debt	122,000	93,500
Principal payments on notes payable and long-term debt	(259,682)	(256,732)
Payment of contingent consideration recorded at acquisition date	(542)	(2,743)
Change in book overdraft	18	(90)
Proceeds from option and warrant exercises	2,958	1,330
Excess tax benefit associated with equity-based compensation	7,096	2,667
Payments for cash dividends	(28,496)	(24,654)
Tax withholdings related to net share settlements of restricted stock units	(6,729)	(5,362)
Distributions to noncontrolling interests	(371)	(198)
Debt issuance costs	(125)	(1,920)
Net cash used in financing activities	(163,873)	(194,202)
Net increase (decrease) in cash and equivalents	7,813	(7,000)
Cash and equivalents at beginning of period	13,591	23,212
Cash and equivalents at end of period	21,404	16,212
Non-cash financing activity:
Liabilities assumed and notes payable issued to sellers of businesses acquired	$ 3,257	$ 377