Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
OPERATING ACTIVITIES
Net income	$ 20,501	$ 19,056	$ 60,180	$ 50,237
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			71,001	76,086
Deferred income taxes			5,090	8,268
Stock-based compensation			1,570	374
Gain on disposal of property and equipment	(12,595)	(7,156)	(23,978)	(15,410)
Changes in certain working capital items:
Trade receivables			2,884	8,773
Prepaid expenses and other current assets			619	387
Accounts payable, accrued liabilities, and accrued expenses			(9,536)	(18,168)
Accrued income taxes			1,549	(1,900)
Net cash provided by operating activities			109,379	108,647
INVESTING ACTIVITIES
Proceeds from sale of property and equipment			66,350	84,910
Purchases of property and equipment, net of trades			(120,548)	(127,526)
Payments to Acquire Businesses, Net of Cash Acquired			(62,127)	0
Change in other assets			(10)	563
Net cash used in investing activities			(116,335)	(42,053)
FINANCING ACTIVITIES
Payments of cash dividends			(4,922)	(4,950)
Repayments of debt assumed			(39,887)	0
Shares withheld for employee taxes related to stock-based compensation			(415)	(181)
Repurchases of common stock			0	(25,086)
Net cash used in financing activities			(45,224)	(30,217)
Net (decrease) increase in cash, cash equivalents and restricted cash			(52,180)	36,377
CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Beginning of period			182,938	106,098
Ending Period	130,758	142,475	130,758	142,475
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid during the period for income taxes, net of refunds			12,844	4,974
Interest Paid, Excluding Capitalized Interest, Operating Activities			335	0
Noncash investing and financing activities:
Purchased property and equipment in accounts payable			5,562	16,977
Sold revenue equipment in other current assets			6,765	15,900
RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Cash and Cash Equivalents, at Carrying Value	111,934	120,000	111,934	120,000
Restricted Cash and Investments, Current	2,040	3,298	2,040	3,298
Restricted Cash and Cash Equivalents, Noncurrent	16,784	19,177	16,784	19,177
Ending Period	$ 130,758	$ 142,475	$ 130,758	$ 142,475