NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Lease Accounting (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
LEASE
Practical expedient, remaining performance obligation option			true
Revenue, practical expedient, incremental costs of obtaining or fulfilling a contract			true
Adopt the land easement practical expedient			true
Practical expedient separate non lease from lease components	true		true
Lessee operating lease existence of option to extend			true
Lessee finance lease existence of option to extend			true
Finance lease right-of-use assets	$ 29.2		$ 29.2		$ 25.3
Depreciation	21.0	$ 35.8	45.5	$ 73.0
Asset Leased Under Operating Leases
LEASE
Depreciation	4.2	3.9	8.3	8.8
Lease income	$ 6.2	$ 6.1	$ 12.4	$ 11.6
Maximum
LEASE
Operating lease, renewal terms	5 years		5 years
Finance lease, renewal terms	5 years		5 years
Maximum | Real estate
LEASE
Operating lease, initial terms	15 years		15 years
Finance Lease, initial terms	15 years		15 years
Maximum | Revenue equipment
LEASE
Operating lease, initial terms	9 years		9 years
Finance Lease, initial terms	9 years		9 years
Maximum | Asset Leased Under Operating Leases
LEASE
Operating lease, initial terms	72 months		72 months
Minimum
LEASE
Operating lease, renewal terms	1 year		1 year
Finance lease, renewal terms	1 year		1 year
Minimum | Real estate
LEASE
Operating lease, initial terms	3 years		3 years
Finance Lease, initial terms	3 years		3 years
Minimum | Revenue equipment
LEASE
Operating lease, initial terms	3 years		3 years
Finance Lease, initial terms	3 years		3 years
Minimum | Asset Leased Under Operating Leases
LEASE
Terms	30 months		30 months