Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 57,318	$ 87,066
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	152,849	143,065
Deferred income taxes	23,773	(3,417)
Gain on disposal of property and equipment	(13,250)	(18,880)
Non-cash equity compensation	2,325	3,607
Insurance and claims accruals, net of current portion	(11,070)	6,450
Other	(8,500)	5,288
Changes in certain working capital items:
Accounts receivable, net	(1,489)	15,849
Other current assets	(11,647)	29,546
Accounts payable	1,898	10,163
Other current liabilities	8,968	4,035
Net cash provided by operating activities	201,175	282,772
Cash flows from investing activities:
Additions to property and equipment	(388,386)	(337,475)
Proceeds from sales of property and equipment	94,372	86,366
Decrease in notes receivable	14,007	11,956
Net cash used in investing activities	(280,007)	(239,153)
Cash flows from financing activities:
Repayments of short-term debt	(20,000)	0
Proceeds from issuance of short-term debt	20,000	0
Repayments of long-term debt	(40,000)	0
Proceeds from issuance of long-term debt	115,000	0
Change in net checks issued in excess of cash balances	2,665	0
Dividends on common stock	(12,966)	(10,801)
Repurchases of common stock	0	(6,438)
Tax withholding related to net share settlements of restricted stock awards	(623)	(461)
Stock options exercised	298	846
Excess tax benefits from equity compensation	(17)	219
Payment of notes payable	(3,117)	(3,117)
Net cash provided by (used in) financing activities	61,240	(19,752)
Effect of exchange rate fluctuations on cash	(505)	(550)
Net increase (decrease) in cash and cash equivalents	(18,097)	23,317
Cash and cash equivalents, beginning of period	31,833	22,604
Cash and cash equivalents, end of period	13,736	45,921
Supplemental disclosures of cash flow information:
Interest paid	1,838	1,578
Income taxes paid	4,257	34,201
Supplemental schedule of non-cash investing activities:
Notes receivable issued upon sale of property and equipment	22,952	21,792
Change in fair value of interest rate swap	(517)	(368)
Property and equipment acquired included in accounts payable	821	10,513
Property and equipment disposed included in other receivables	$ 259	$ 0