Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
OPERATING ACTIVITIES
Net income	$ 16,775	$ 13,734
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	23,311	26,983
Deferred income taxes	(1,744)	(3,390)
Stock-based compensation	271	581
Gain on disposal of property and equipment	(4,258)	(4,232)
Changes in certain working capital items:
Trade receivables	(8,771)	(4,991)
Prepaid expenses and other current assets	1,083	4,053
Accounts payable, accrued liabilities, and accrued expenses	3,557	(2,554)
Accrued income taxes	7,369	5,248
Net cash provided by operating activities	37,593	35,432
INVESTING ACTIVITIES
Proceeds from sale of property and equipment	13,648	25,152
Purchases of property and equipment	(22,029)	(9,750)
Change in other assets	0	78
Net cash provided by (used in) investing activities	(8,381)	15,480
FINANCING ACTIVITIES
Payments of cash dividends	0	(1,599)
Shares withheld for employee taxes related to stock-based compensation	(41)	(96)
Repurchases of common stock	0	(15,022)
Net cash used in financing activities	(41)	(16,717)
Net increase in cash, cash equivalents and restricted cash	29,171	34,195
CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Beginning of period	173,767	131,140
Ending Period	202,938	165,335
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Cash paid during the period for income taxes, net of refunds	142	2,825
Noncash investing and financing activities:
Purchased property and equipment in accounts payable	2,058	6,726
Sold revenue equipment and property in other current assets	1,213	212
Common stock dividends declared in accounts payable	1,579	0
RECONCILIATION OF CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Cash and Cash Equivalents, at Carrying Value	187,085	148,212
Restricted Cash and Investments, Current	916	1,033
Restricted Cash and Cash Equivalents, Noncurrent	14,937	16,090
Ending Period	$ 202,938	$ 165,335