Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net income	$ 87,066	$ 65,941
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	143,065	131,878
Deferred income taxes	(3,417)	(16,206)
Gain on disposal of property and equipment	(18,880)	(14,267)
Non-cash equity compensation	3,607	4,350
Insurance and claims accruals, net of current portion	6,450	(1,075)
Other	5,288	(3,481)
Changes in certain working capital items:
Accounts receivable, net	15,849	(32,759)
Other current assets	29,546	1,592
Accounts payable	10,163	24,356
Other current liabilities	4,035	4,882
Net cash provided by operating activities	282,772	165,211
Cash flows from investing activities:
Additions to property and equipment	(337,475)	(206,354)
Proceeds from sales of property and equipment	86,366	59,515
Decrease in notes receivable	11,956	11,135
Other	0	(3,343)
Net cash used in investing activities	(239,153)	(139,047)
Cash flows from financing activities:
Repayments of long-term debt	0	(40,000)
Proceeds from issuance of long-term debt	0	75,000
Dividends on common stock	(10,801)	(10,853)
Repurchases of common stock	(6,438)	(30,587)
Tax withholding related to net share settlements of restricted stock awards	(461)	(96)
Stock options exercised	846	4,169
Excess tax benefits from equity compensation	219	295
Payment of notes payable	(3,117)	0
Net cash used in financing activities	(19,752)	(2,072)
Effect of exchange rate fluctuations on cash	(550)	(172)
Net increase in cash and cash equivalents	23,317	23,920
Cash and cash equivalents, beginning of period	22,604	23,678
Cash and cash equivalents, end of period	45,921	47,598
Supplemental disclosures of cash flow information:
Interest paid	1,578	304
Income taxes paid	34,201	59,070
Supplemental schedule of non-cash investing activities:
Notes receivable issued upon sale of property and equipment	21,792	9,427
Issuance of notes payable	0	6,233
Change in fair value of interest rate swap	(368)	(431)
Property and equipment acquired included in accounts payable	10,513	460
Property and equipment disposed included in other receivables	$ 0	$ 351