Consolidated Balance Sheets - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 5,566,000	$ 5,961,000
Trade accounts receivable, net	654,542,000	653,795,000
Inventories	23,191,000	27,740,000
Prepaid licenses and permits	25,057,000	22,886,000
Prepaid insurance	60,599,000	55,660,000
Other current assets	90,412,000	95,457,000
Total current assets	859,367,000	861,499,000
Property and equipment, at cost:
Revenue and service equipment	3,636,767,000	3,336,529,000
Land	39,026,000	38,978,000
Structures and improvements	154,142,000	153,704,000
Furniture and office equipment	189,516,000	190,546,000
Total property and equipment	4,019,451,000	3,719,757,000
Less accumulated depreciation	1,318,122,000	1,237,225,000
Net property and equipment	2,701,329,000	2,482,532,000
Other assets	75,871,000	34,455,000
Total assets	$ 3,636,567,000	3,378,486,000
Current liabilities:
Current portion of long-term debt		250,000,000
Trade accounts payable	$ 340,332,000	325,838,000
Claims accruals	104,220,000	96,719,000
Accrued payroll	59,420,000	80,547,000
Other accrued expenses	28,445,000	17,966,000
Total current liabilities	532,417,000	771,070,000
Long-term debt	1,005,026,000	683,539,000
Other long-term liabilities	58,552,000	59,561,000
Deferred income taxes	740,220,000	659,793,000
Total liabilities	$ 2,336,215,000	$ 2,173,963,000
Commitments and contingencies (Note 10)
Stockholders’ equity:
Preferred stock, $100 par value. 10 million shares authorized; none outstanding	$ 0	$ 0
Common stock, $.01 par value. 1 billion shares authorized; (167,099,432 shares issued at December 31, 2015 and 2014, of which 113,947,780 shares and 116,575,163 shares were outstanding at December 31, 2015 and 2014, respectively)	1,671,000	1,671,000
Additional paid-in capital	268,728,000	247,641,000
Retained earnings	2,885,843,000	2,555,972,000
Treasury stock, at cost (53,151,652 shares at December 31, 2015, and 50,524,269 shares at December 31, 2014)	(1,855,890,000)	(1,600,761,000)
Total stockholders’ equity	1,300,352,000	1,204,523,000
Total liabilities and stockholders' equity	$ 3,636,567,000	$ 3,378,486,000