Consolidated Condensed Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 19,315	$ 13,650
Receivables:
Trade, net	70,306	70,869
Other	2,212	4,142
Prepaid expenses and other	13,366	15,274
Deferred income taxes	3,479	3,415
Total current assets	108,678	107,350
Property and equipment:
Accumulated depreciation	(171,886)	(164,916)
Net property and equipment	424,145	415,009
Other assets	3,489	3,443
TOTAL ASSETS	536,312	525,802
Current liabilities:
Accounts payable and accrued liabilities	42,467	38,624
Insurance and claims accruals	14,847	14,404
Total current liabilities	57,314	53,028
Deferred income taxes	114,777	113,637
Total liabilities	172,091	166,665
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; 48,000,000 shares authorized; 33,349,150 shares at March 31, 2014, and 33,301,048 shares at December 31, 2013, issued and outstanding	333	333
Additional paid-in capital	85,708	85,077
Retained earnings	278,180	273,727
Total stockholders’ equity	364,221	359,137
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	536,312	525,802
Office Equipment And Other [Member]
Property and equipment:
Revenue equipment, buildings and land, office equipment and other	$ 596,031	$ 579,925