Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 5,961	$ 5,831
Trade accounts receivable, net	653,795	568,519
Inventories	27,740	26,248
Prepaid licenses and permits	22,886	21,602
Prepaid insurance	55,660	42,588
Deferred income taxes	18,631
Other current assets	95,457	15,415
Total current assets	880,130	680,203
Property and equipment, at cost:
Revenue and service equipment	3,336,529	2,904,289
Land	38,978	37,829
Structures and improvements	153,704	144,439
Furniture and office equipment	190,546	173,257
Total property and equipment	3,719,757	3,259,814
Less accumulated depreciation	1,237,225	1,147,610
Net property and equipment	2,482,532	2,112,204
Other assets	34,455	26,997
Total assets	3,397,117	2,819,404
Current liabilities:
Current portion of long-term debt	250,000	250,000
Trade accounts payable	325,838	305,465
Claims accruals	96,719	68,221
Accrued payroll	80,547	72,063
Other accrued expenses	17,966	14,062
Deferred income taxes		2,485
Total current liabilities	771,070	712,296
Long-term debt	683,539	458,417
Other long-term liabilities	59,561	58,274
Deferred income taxes	678,424	577,965
Total liabilities	2,192,594	1,806,952
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, 2014 and 2013, of which 116,575,163 shares and 117,241,438 shares were outstanding at December 31, 2014 and 2013, respectively)	1,671	1,671
Additional paid-in capital	247,641	226,595
Retained earnings	2,555,972	2,274,784
Treasury stock, at cost (50,524,269 shares at December 31, 2014, and 49,857,994 shares at December 31, 2013)	(1,600,761)	(1,490,598)
Total stockholders’ equity	1,204,523	1,012,452
Total liabilities and stockholders' equity	$ 3,397,117	$ 2,819,404