NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2019
INCOME TAXES
Uncertain tax positions	$ 0.0		$ 0.0
Customer relationships
Goodwill and Intangible Assets
Estimated useful lives	9 years 2 months 12 days
Customer relationships | Minimum
Goodwill and Intangible Assets
Estimated useful lives	10 years
Customer relationships | Maximum
Goodwill and Intangible Assets
Estimated useful lives	15 years
Non-competition agreements
Goodwill and Intangible Assets
Estimated useful lives	1 year 10 months 24 days
Non-competition agreements | Minimum
Goodwill and Intangible Assets
Estimated useful lives	2 years
Non-competition agreements | Maximum
Goodwill and Intangible Assets
Estimated useful lives	5 years
Trade names
Goodwill and Intangible Assets
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)		$ 2.8