Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Operating Activities:
Net income	$ 35,563	$ 26,642
Noncash items included in net income:
Depreciation and amortization	37,765	35,681
Other, net	2,909	1,895
Changes in operating assets and liabilities, net	(8,680)	13,207
Net cash provided by operating activities	67,557	77,425
Investing Activities:
Acquisition of property and equipment	(100,799)	(81,888)
Proceeds from disposal of property and equipment	3,058	2,609
Acquisition of business, net of cash		(7,616)
Net cash used in investing activities	(97,741)	(86,895)
Financing Activities:
Repayment of revolving credit agreement	(166,939)	(262,251)
Borrowing of revolving credit agreement	208,811	281,642
Proceeds from stock option exercises	3,708	637
Repayment of senior notes	(11,071)	(11,071)
Other financing activities	(586)
Net cash provided by financing activities	33,923	8,957
Net Increase (Decrease) in Cash and Cash Equivalents	3,739	(513)
Cash and cash equivalents, beginning of period	321	1,317
Cash and cash equivalents, end of period	$ 4,060	$ 804