Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 7,082	$ 14,612
Trade accounts receivable, net	900,903	920,767
Prepaid expenses and other	328,079	403,349
Total current assets	1,236,064	1,338,728
Property and equipment, at cost	4,764,722	4,670,464
Less accumulated depreciation	1,720,446	1,687,133
Net property and equipment	3,044,276	2,983,331
Other assets	141,317	143,290
Total assets	4,421,657	4,465,349
Current liabilities:
Current portion of long-term debt	247,609
Trade accounts payable	503,829	598,594
Claims accruals	256,896	251,980
Accrued payroll	58,599	42,382
Other accrued expenses	25,583	28,888
Total current liabilities	1,092,516	921,844
Long-term debt	752,423	1,085,649
Other long-term liabilities	88,373	76,661
Deferred income taxes	545,282	541,870
Stockholders' equity	1,943,063	1,839,325
Total liabilities and stockholders' equity	$ 4,421,657	$ 4,465,349