Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 56,995	$ 66,127
Trade, less allowance of $348 as of each date	99,003	83,426
Other	6,971	4,202
Prepaid expenses and other	23,980	21,903
Total current assets	186,949	175,658
Property and equipment:
Less accumulated depreciation	(274,199)	(275,950)
Net property and equipment	682,277	654,173
Other noncurrent assets	1,464	1,805
Total assets	870,690	831,636
Current liabilities:
Accounts payable	20,150	25,702
Insurance and claims accruals	42,014	39,595
Accrued and other current liabilities	31,395	24,497
Total current liabilities	93,559	89,794
Deferred income taxes	125,163	121,098
Noncurrent operating lease liabilities	291	411
Total liabilities	219,013	211,303
Commitments and contingencies (Note 15)
Stockholders’ equity:
Preferred stock, $.01 par value per share; 2,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $.01 par value per share; 192,000,000 shares authorized; 83,034,404 shares at December 31, 2021, and 82,705,005 shares at December 31, 2020, issued and outstanding	830	827
Additional paid-in capital	85,718	85,070
Retained earnings	565,129	534,436
Total stockholders’ equity	651,677	620,333
Total liabilities and stockholders’ equity	870,690	831,636
Revenue Equipment [Member]
Property and equipment:
Property and equipment	810,711	787,780
Land and Building [Member]
Property and equipment:
Property and equipment	92,824	90,049
Office Equipment [Member]
Property and equipment:
Property and equipment	$ 52,941	$ 52,294