Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 261,478	$ 169,078	$ 166,944
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	267,700	263,286	249,527
Deferred income taxes	29,488	(10,233)	16,401
Gain on disposal of property and equipment	(60,528)	(11,271)	(21,557)
Non-cash equity compensation	10,807	8,903	8,077
Insurance and claims accruals, net of current portion	5,582	3,420	14,188
Other	(3,105)	13,641	(3,360)
Gains on investment in equity securities	(40,317)	0	0
Changes in certain working capital items:
Accounts receivable, net	(101,007)	(18,258)	15,081
Other current assets	(27,903)	(7,390)	975
Accounts payable	14,742	(2,483)	(7,537)
Other current liabilities	(24,118)	37,216	(12,095)
Net cash provided by operating activities	332,819	445,909	426,644
Cash flows from investing activities:
Additions to property and equipment	(370,850)	(413,065)	(420,748)
Proceeds from sales of property and equipment	177,801	146,824	136,873
Net cash invested in acquisitions	(201,845)	0	0
Investment in equity securities	10,000	5,000	0
Decrease in notes receivable	7,593	7,966	11,566
Net cash used in investing activities	(397,301)	(263,275)	(272,309)
Cash flows from financing activities:
Repayments of short-term debt	27,500	90,000	0
Proceeds from issuance of short-term debt	5,000	40,000	0
Repayments of long-term debt	0	50,000	100,000
Proceeds from issuance of long-term debt	250,000	0	275,000
Dividends on common stock	(29,083)	(24,888)	(286,190)
Repurchases of common stock	(104,444)	(56,521)	(42,301)
Tax withholding related to net share settlements of restricted stock awards	(4,270)	(4,553)	(1,899)
Stock options exercised	0	0	171
Distribution to noncontrolling interest	(35)	0	0
Net cash provided by (used in) financing activities	89,668	(185,962)	(155,219)
Effect of exchange rate fluctuations on cash	(324)	(780)	396
Net increase (decrease) in cash, cash equivalents and restricted cash	24,862	(4,108)	(488)
Cash, cash equivalents and restricted cash, beginning of period	29,334	33,442	33,930
Cash, cash equivalents and restricted cash, end of period	54,196	29,334	33,442
Supplemental disclosures of cash flow information:
Interest paid	4,228	4,415	6,441
Income taxes paid	81,185	54,173	49,599
Supplemental schedule of non-cash investing and financing activities:
Notes receivable issued upon sale of property and equipment	5,953	3,441	6,764
Change in fair value of interest rate swaps	3,610	(5,238)	(651)
Property and equipment acquired included in accounts payable	7,124	12,250	21,138
Property and equipment disposed included in other receivables	0	30	18,600
Dividends accrued but not yet paid at end of period	7,895	6,114	6,232
Noncontrolling interest associated with acquisition	33,556	0	0
Contingent consideration associated with acquisition	2,500	0	0
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	54,196	29,334	26,418
Restricted cash included in other current assets	0	0	7,024
Cash, cash equivalents and restricted cash, end of period	$ 54,196	$ 29,334	$ 33,442