Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 61,755	$ 57,318
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	162,619	152,849
Deferred income taxes	6,492	23,773
Gain on disposal of property and equipment	(6,031)	(13,250)
Non-cash equity compensation	3,215	2,325
Insurance and claims accruals, net of current portion	(6,645)	(11,070)
Other	(8,755)	(8,500)
Changes in certain working capital items:
Accounts receivable, net	(18,344)	(1,489)
Other current assets	15,184	(11,647)
Accounts payable	7,107	1,898
Other current liabilities	351	8,968
Net cash provided by operating activities	216,948	201,175
Cash flows from investing activities:
Additions to property and equipment	(205,874)	(388,386)
Proceeds from sales of property and equipment	84,769	94,372
Issuance of notes receivable	(5,000)	0
Decrease in notes receivable	15,637	14,007
Net cash used in investing activities	(110,468)	(280,007)
Cash flows from financing activities:
Repayments of short-term debt	(45,000)	(20,000)
Proceeds from issuance of short-term debt	0	20,000
Repayments of long-term debt	(60,000)	(40,000)
Proceeds from issuance of long-term debt	0	115,000
Change in net checks issued in excess of cash balances	3,538	2,665
Dividends on common stock	(13,721)	(12,966)
Tax withholding related to net share settlements of restricted stock awards	(445)	(623)
Stock options exercised	2,339	298
Excess tax benefits from equity compensation	0	(17)
Payment of notes payable	0	(3,117)
Net cash provided by (used in) financing activities	(113,289)	61,240
Effect of exchange rate fluctuations on cash	580	(505)
Net decrease in cash and cash equivalents	(6,229)	(18,097)
Cash and cash equivalents, beginning of period	16,962	31,833
Cash and cash equivalents, end of period	10,733	13,736
Supplemental disclosures of cash flow information:
Interest paid	2,004	1,838
Income taxes paid	15,819	4,257
Supplemental schedule of non-cash investing activities:
Notes receivable issued upon sale of property and equipment	4,058	22,952
Change in fair value of interest rate swap	334	(517)
Property and equipment acquired included in accounts payable	492	821
Property and equipment disposed included in other receivables	$ 1,300	$ 259