INCOME TAXES - Effective income tax and the U.S. statutory income tax rate (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective income tax rate and the U.S. statutory income tax rate
Income tax expense (benefit) at U.S. statutory income tax rate									$ (76.1)	$ (4.4)	$ (8.8)
Federal income tax effects of:
State income tax expense									(6.2)	(2.7)	(0.3)
Foreign taxes											(0.2)
Foreign tax rate differential									(0.8)	(0.3)	0.1
Goodwill impairment									23.4
Per diem and other nondeductible expenses									2.3	4.1	3.2
Change in valuation allowance									1.2
Cumulative effect of change in effective tax rate										(12.6)	(46.1)
Tax credits									(0.3)	(0.1)	(0.1)
Other									1.9	0.1	(0.1)
Provision (benefit) for income taxes	$ 5.8	$ (57.8)	$ (0.7)	$ (1.9)	$ (1.7)	$ 0.7	$ (14.5)	$ (0.4)	$ (54.6)	$ (15.9)	$ (52.3)
Effective tax rate									15.10%	75.40%	206.80%
Federal income tax rate									21.00%	21.00%	35.00%