SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) School State Campus Segment Unit	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Business Activities [Abstract]
Number of schools | School	22
Number of states in which schools operate across the United States | State	14
Number of campuses treated as destination schools | Campus	5
Number of reportable segments | Segment	3
Liquidity [Abstract]
Cash, cash equivalents and restricted cash	$ 38,026	$ 38,644	$ 45,946
Cash balance	20,800	4,600
Line of credit facility, remaining borrowing capacity	$ 21,000
Cash and Cash Equivalents [Abstract]
Maximum maturity period for classification of cash equivalents	3 months
Restricted Cash [Abstract]
Restricted cash in long-term assets	$ 0	15,000
Advertising Costs [Abstract]
Advertising expense	$ 31,200	29,800
Goodwill and Other Intangible Assets [Abstract]
Number of reporting units | Unit	9
Number of reporting units failing to achieve projected operating results | Unit	1
Amount of goodwill impairment	$ 0	0
Impairment of Long-Lived Assets [Abstract]
Impairment of long-lived assets	0	0
Concentration of Credit Risk [Abstract]
Federal deposit insurance limit	250
Excess cash, FDIC uninsured amount	37,750
Income Taxes [Abstract]
Interest and penalties expense	$ 0	$ 0