LEASES - Components of lease expenses (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Lease cost
Total operating lease cost	$ 36.0
Interest on lease liabilities	0.9
Total finance lease cost	6.3
Total lease cost	42.3
Operations and maintenance | Revenue equipment
Lease cost
Total operating lease cost	22.2
Administrative expense | Real estate
Lease cost
Total operating lease cost	13.8
Depreciation and amortization
Lease cost
Amortization right-of-use assets	5.4
Interest Expense
Lease cost
Interest on lease liabilities	$ 0.9