Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net income	$ 118,524	$ 62,190
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	127,816	136,507
Deferred income taxes	15,036	(2,896)
Gain on disposal of property and equipment	(24,008)	(3,411)
Non-cash equity compensation	5,249	3,544
Insurance and claims accruals, net of current portion	4,632	6,601
Other	842	11,036
Gains on investment in equity securities	(20,191)	0
Changes in certain working capital items:
Accounts receivable, net	(49,978)	23,463
Other current assets	3,144	14,515
Accounts payable	16,639	(1,323)
Other current liabilities	(8,241)	37,116
Net cash provided by operating activities	189,464	287,342
Cash flows from investing activities:
Additions to property and equipment	(192,983)	(170,235)
Proceeds from sales of property and equipment	90,036	62,626
Investment in equity securities	(5,000)	0
Decrease in notes receivable	3,342	4,392
Net cash used in investing activities	(104,605)	(103,217)
Cash flows from financing activities:
Repayments of short-term debt	(25,000)	(75,000)
Proceeds from issuance of short-term debt	5,000	0
Repayments of long-term debt	0	(50,000)
Proceeds from issuance of long-term debt	120,000	0
Dividends on common stock	(12,906)	(12,450)
Repurchases of common stock	(5,507)	(8,798)
Tax withholding related to net share settlements of restricted stock awards	(3,740)	(3,935)
Net cash provided by (used in) financing activities	77,847	(150,183)
Effect of exchange rate fluctuations on cash	88	(1,995)
Net increase (decrease) in cash, cash equivalents and restricted cash	162,794	31,947
Cash, cash equivalents and restricted cash, beginning of period	29,334	33,442
Cash, cash equivalents and restricted cash, end of period	192,128	65,389
Supplemental disclosures of cash flow information:
Interest paid	1,583	2,996
Income taxes paid	40,047	2,992
Supplemental schedule of non-cash investing and financing activities:
Notes receivable issued upon sale of property and equipment	2,646	1,429
Change in fair value of interest rate swaps	1,663	(6,220)
Property and equipment acquired included in accounts payable	6,715	12,090
Property and equipment disposed included in other receivables	32	1,982
Dividends accrued but not yet paid at end of period	$ 8,151	$ 6,219