Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities:
Net income	$ 128,644	$ 118,524
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	135,700	127,816
Deferred income taxes	(630)	15,036
Gain on disposal of property and equipment	(41,138)	(24,008)
Non-cash equity compensation	6,085	5,249
Insurance and claims accruals, net of current portion	4,874	4,632
Other	(4,142)	842
Gain on investments in equity securities, net	(14,289)	(20,191)
Changes in certain working capital items:
Accounts receivable, net	(21,125)	(49,978)
Other current assets	20,728	3,144
Accounts payable	30,091	16,639
Other current liabilities	22,729	(8,241)
Net cash provided by operating activities	267,527	189,464
Cash flows from investing activities:
Additions to property and equipment	(227,334)	(192,983)
Proceeds from sales of property and equipment	73,911	90,036
Net cash invested in acquisition	705	0
Investment in equity securities	(20,250)	(5,000)
Decrease in notes receivable	3,288	3,342
Net cash used in investing activities	(169,680)	(104,605)
Cash flows from financing activities:
Repayments of short-term debt	(2,500)	(25,000)
Proceeds from issuance of short-term debt	0	5,000
Repayments of long-term debt	(100,000)	0
Proceeds from issuance of long-term debt	120,000	120,000
Change in checks issued in excess of cash balances	6,032	0
Dividends on common stock	(15,702)	(12,906)
Repurchases of common stock	(102,113)	(5,507)
Tax withholding related to net share settlements of restricted stock awards	(3,658)	(3,740)
Net cash provided by (used in) financing activities	(97,941)	77,847
Effect of exchange rate fluctuations on cash	322	88
Net increase in cash and cash equivalents	228	162,794
Cash and cash equivalents, beginning of period	54,196	29,334
Cash and cash equivalents, end of period	54,424	192,128
Supplemental disclosures of cash flow information:
Interest paid	3,236	1,583
Income taxes paid	31,096	40,047
Supplemental schedule of non-cash investing and financing activities:
Notes receivable issued upon sale of property and equipment	2,350	2,646
Change in fair value of interest rate swaps	4,914	1,663
Property and equipment acquired included in accounts payable	8,431	6,715
Property and equipment disposed included in other receivables	1,205	32
Dividends accrued but not yet paid at end of period	$ 8,244	$ 8,151