Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities:
Net income	$ 86,785	$ 103,034	$ 102,757
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	173,019	166,957	158,634
Deferred income taxes	(8,389)	(9,068)	57,863
Gain on disposal of property and equipment	(16,408)	(20,533)	(21,290)
Non-cash equity compensation	4,809	4,602	2,599
Insurance and claims accruals, net of current portion	6,400	4,250	8,000
Other	(541)	(237)	(1,073)
Changes in certain working capital items:
Accounts receivable, net	(20,514)	7,579	(28,448)
Other current assets	3,398	17,581	(21,744)
Accounts payable	2,793	(20,172)	19,381
Other current liabilities	1,105	1,103	(12,199)
Net cash provided by operating activities	232,457	255,096	264,480
Cash flows from investing activities:
Additions to property and equipment	(211,329)	(284,942)	(302,340)
Retirements of property and equipment	59,413	60,015	70,142
Decrease in notes receivable	10,679	8,122	7,354
Other	979	0	0
Net cash used in investing activities	(140,258)	(216,805)	(224,844)
Cash flows from financing activities:
Repayments of short-term debt	(20,000)	(160,000)	(50,000)
Proceeds from issuance of short-term debt	0	180,000	50,000
Repayments of Long-term Lines of Credit	40,000
Repayments of long-term debt		0	0
Proceeds from issuance of long-term debt	10,000	70,000	0
Change in net checks issued in excess of cash balances	0	(6,671)	6,671
Dividends on common stock	(14,587)	(124,391)	(50,969)
Repurchases of common stock	(20,060)	0	0
Tax withholding related to net share settlements of restricted stock awards	(1,804)	(674)	0
Stock options exercised	2,548	6,035	2,940
Excess tax benefits from equity compensation	379	150	605
Net cash used in financing activities	(83,524)	(35,551)	(40,753)
Effect of exchange rate fluctuations on cash	(425)	276	(437)
Net increase (decrease) in cash and cash equivalents	8,250	3,016	(1,554)
Cash and cash equivalents, beginning of period	15,428	12,412	13,966
Cash and cash equivalents, end of period	23,678	15,428	12,412
Supplemental disclosures of cash flow information:
Interest paid	466	245	85
Income taxes paid	66,032	67,968	28,802
Supplemental schedule of non-cash investing activities:
Notes receivable issued upon sale of property and equipment	17,110	10,564	9,172
Property and equipment acquired included in accounts payable	5,403	109	17,026
Property and equipment disposed included in other receivables	$ 434	$ 311	$ 258