Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 15,191	$ 14,612
Trade accounts receivable, net	1,019,622	920,767
Prepaid expenses and other	272,608	403,349
Total current assets	1,307,421	1,338,728
Property and equipment, at cost	4,924,684	4,670,464
Less accumulated depreciation	1,782,297	1,687,133
Net property and equipment	3,142,387	2,983,331
Other assets, net	139,435	143,290
Total assets	4,589,243	4,465,349
Current liabilities:
Current portion of long-term debt	249,436
Trade accounts payable	551,715	598,594
Claims accruals	259,078	251,980
Accrued payroll	63,792	42,382
Other accrued expenses	34,516	28,888
Total current liabilities	1,158,537	921,844
Long-term debt	755,575	1,085,649
Other long-term liabilities	88,903	76,661
Deferred income taxes	552,866	541,870
Stockholders' equity	2,033,362	1,839,325
Total liabilities and stockholders' equity	$ 4,589,243	$ 4,465,349