Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income	$ 46,492	$ 23,058
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	63,951	68,837
Deferred income taxes	3,487	(2,912)
Gain on disposal of property and equipment	(10,520)	(2,469)
Non-cash equity compensation	2,502	2,406
Insurance and claims accruals, net of current portion	4,212	5,973
Other	1,285	88
Changes in certain working capital items:
Accounts receivable, net	(6,798)	11,946
Other current assets	551	12,195
Accounts payable	18,481	354
Other current liabilities	12,224	13,900
Net cash provided by operating activities	135,867	133,376
Cash flows from investing activities:
Additions to property and equipment	(82,555)	(57,231)
Proceeds from sales of property and equipment	44,689	38,391
Investment in equity securities	(5,000)	0
Decrease in notes receivable	1,575	2,316
Net cash used in investing activities	(41,291)	(16,524)
Cash flows from financing activities:
Repayments of short-term debt	(25,000)	0
Repayments of long-term debt	0	(50,000)
Dividends on common stock	(6,114)	(6,232)
Repurchases of common stock	(5,507)	(8,798)
Tax withholding related to net share settlements of restricted stock awards	(3,740)	(3,930)
Net cash used in financing activities	(40,361)	(68,960)
Effect of exchange rate fluctuations on cash	(419)	(2,073)
Net increase (decrease) in cash, cash equivalents and restricted cash	53,796	45,819
Cash, cash equivalents and restricted cash, beginning of period	29,334	33,442
Cash, cash equivalents and restricted cash, end of period	83,130	79,261
Supplemental disclosures of cash flow information:
Interest paid	878	1,811
Income taxes paid	536	611
Supplemental schedule of non-cash investing and financing activities:
Notes receivable issued upon sale of property and equipment	988	1,099
Change in fair value of interest rate swaps	1,303	(5,597)
Property and equipment acquired included in accounts payable	23,570	13,848
Property and equipment disposed included in other receivables	17	1,251
Dividends accrued but not yet paid at end of period	6,792	6,218
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	83,130	72,237
Restricted cash included in other current assets	0	7,024
Cash, cash equivalents and restricted cash, end of period	$ 83,130	$ 79,261