Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net income	$ 79,404	$ 66,071
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	122,196	112,057
Deferred income taxes	1,088	16,269
Gain on disposal of property and equipment	(10,383)	(11,346)
Non-cash equity compensation	4,365	3,389
Insurance and claims accruals, net of current portion	11,967	14,081
Other	(3,365)	(2,795)
Changes in certain working capital items:
Accounts receivable, net	6,688	(28,960)
Other current assets	7,028	3,791
Accounts payable	5,554	10,745
Other current liabilities	(4,206)	(851)
Net cash provided by operating activities	220,336	182,451
Cash flows from investing activities:
Additions to property and equipment	(239,289)	(256,202)
Proceeds from sales of property and equipment	76,936	81,367
Issuance of notes receivable	0	(3,300)
Decrease in notes receivable	6,505	11,727
Net cash used in investing activities	(155,848)	(166,408)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	265,000	20,000
Change in net checks issued in excess of cash balances	0	(7,842)
Dividends on common stock	(273,734)	(10,140)
Repurchases of common stock	(42,301)	(22,884)
Tax withholding related to net share settlements of restricted stock awards	(1,189)	(679)
Stock options exercised	0	248
Net cash used in financing activities	(52,224)	(21,297)
Effect of exchange rate fluctuations on cash	226	47
Net increase (decrease) in cash, cash equivalents and restricted cash	12,490	(5,207)
Cash, cash equivalents and restricted cash, beginning of period	33,930	15,131
Cash, cash equivalents and restricted cash, end of period	46,420	9,924
Supplemental disclosures of cash flow information:
Interest paid	1,830	972
Income taxes paid	36,805	5,463
Supplemental schedule of non-cash investing and financing activities:
Notes receivable issued upon sale of property and equipment	3,732	3,816
Change in fair value of interest rate swap	(211)	372
Property and equipment acquired included in accounts payable	6,126	7,697
Property and equipment disposed included in other receivables	0	265
Dividends accrued but not yet paid at end of period	$ 6,227	$ 6,466