COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Letter of credit
Operating Leased Assets [Line Items]
Outstanding letters of credit	$ 10.6
Revenue Equipment
Operating Leased Assets [Line Items]
Rent expense	4.4	$ 3.9
Office and Terminals
Operating Leased Assets [Line Items]
Rent expense	$ 2.7	$ 0.8

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

No definition available.

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration