ACCRUED EXPENSES (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
ACCRUED EXPENSES
Workers' compensation, third-party casualty, and loss and damage claims reserves	$ 96,159	$ 96,183
Accrued vacation pay	33,731	33,029
Accrued compensation	27,524	35,305
Taxes other than income	7,971	8,022
Other	23,342	22,135
Total accrued expenses	$ 188,727	$ 194,674