Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
OPERATING ACTIVITIES
Net Income	$ 20,714	$ 20,501	$ 53,134	$ 60,180
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			81,786	71,001
Deferred income taxes			9,256	5,090
Stock-based compensation			1,509	1,570
Gain on disposal of property and equipment	(5,721)	(12,595)	(8,739)	(23,978)
Changes in certain working capital items:
Trade receivables			(5,785)	2,884
Prepaid expenses and other current assets			(6,645)	619
Accounts payable, accrued liabilities, and accrued expenses			5,101	(9,536)
Accrued income taxes			3,370	1,549
Net cash provided by operating activities			132,987	109,379
INVESTING ACTIVITIES
Proceeds from sale of property and equipment			51,473	66,350
Purchases of property and equipment			(163,824)	(120,548)
Payments to Acquire Businesses, Net of Cash Acquired			0	(62,127)
Change in other assets			72	(10)
Net cash used in investing activities			(112,279)	(116,335)
FINANCING ACTIVITIES
Payments of cash dividends			(4,884)	(4,922)
Shares withheld for employee taxes related to stock-based compensation			(431)	(415)
Repayments of Assumed Debt			0	(39,887)
Repurchases of common stock			(12,278)	0
Net cash used in financing activities			(17,593)	(45,224)
Net increase (decrease) in cash, cash equivalents and restricted cash			3,115	(52,180)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Beginning of period			96,076	182,938
Ending Period	99,191	130,758	99,191	130,758
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid during the period for income taxes, net of refunds			4,598	12,844
Interest Paid, Excluding Capitalized Interest, Operating Activities			0	335
Noncash investing and financing activities:
Purchased property and equipment in accounts payable			12,114	5,562
Sold revenue equipment and property in other current assets			5,195	6,765
RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Cash and Cash Equivalents, at Carrying Value	81,949	111,934	81,949	111,934
Restricted Cash and Investments, Current	1,097	2,040	1,097	2,040
Restricted Cash and Cash Equivalents, Noncurrent	16,145	16,784	16,145	16,784
Ending Period	$ 99,191	$ 130,758	$ 99,191	$ 130,758