INCOME TAXES - Effective income tax and the U.S. statutory income tax rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective income tax rate and the U.S. statutory income tax rate
Income tax expense (benefit) at United States statutory income tax rate	$ 1.3	$ (76.1)	$ (4.4)
Federal income tax effects of:
State income tax expense, net of federal benefit	(1.6)	(6.2)	(2.7)
Foreign tax rate differential	0.1	(0.8)	(0.3)
Goodwill impairment		23.4
Per diem and other nondeductible expenses	1.4	2.3	4.1
Arbitrated decrease in contingent consideration	(2.9)
Change in valuation allowance	0.6	1.2
Cumulative effect of change in effective tax rate			(12.6)
Tax credits	(0.1)	(0.3)	(0.1)
Other	1.0	1.9	0.1
Benefit for income taxes	$ (0.2)	$ (54.6)	$ (15.9)
Effective tax rate	(3.30%)	15.10%	75.50%