Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net income	$ 54,990	$ 39,971
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	93,984	87,696
Deferred income taxes	(3,097)	(10,753)
Gain on disposal of property and equipment	(12,191)	(9,815)
Non-cash equity compensation	3,755	2,837
Insurance and claims accruals, net of current portion	7,100	350
Other	2,186	(420)
Changes in certain working capital items:
Accounts receivable, net	7,904	(29,658)
Other current assets	28,584	2,097
Accounts payable	16,254	11,238
Other current liabilities	(5,897)	(2,998)
Net cash provided by operating activities	193,572	90,545
Cash flows from investing activities:
Additions to property and equipment	(216,187)	(99,969)
Proceeds from sales of property and equipment	56,781	37,162
Decrease in notes receivable	7,188	8,076
Other	0	(3,343)
Net cash used in investing activities	(152,218)	(58,074)
Cash flows from financing activities:
Dividends on common stock	(7,207)	(7,255)
Repurchases of common stock	(6,438)	(25,602)
Tax withholding related to net share settlements of restricted stock awards	(393)	(31)
Stock options exercised	763	4,150
Excess tax benefits from equity compensation	199	284
Payment of notes payable	(3,117)	0
Net cash used in financing activities	(16,193)	(28,454)
Effect of exchange rate fluctuations on cash	(274)	19
Net increase in cash and cash equivalents	24,887	4,036
Cash and cash equivalents, beginning of period	22,604	23,678
Cash and cash equivalents, end of period	47,491	27,714
Supplemental disclosures of cash flow information:
Interest paid	1,066	233
Income taxes paid	17,862	42,581
Supplemental schedule of non-cash investing activities:
Notes receivable issued upon sale of property and equipment	12,549	6,333
Issuance of notes payable	0	6,233
Change in fair value of interest rate swap	237	0
Property and equipment acquired included in accounts payable	8,967	9,407
Property and equipment disposed included in other receivables	$ 0	$ 696