GOODWILL AND LONG-LIVED ASSETS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
GOODWILL AND LONG-LIVED ASSETS [Abstract]
Impairment of long-lived assets	$ 0	$ 0
Changes in carrying amount of goodwill [Abstract]
Gross Goodwill Balance	117,176	117,176	$ 117,176	$ 117,176
Accumulated Impairment Losses	(102,640)	(102,640)	(102,640)	(102,640)
Adjustments	0	0
Net Goodwill Balance	14,536	14,536	$ 14,536	$ 14,536
Estimated future amortization expense [Abstract]
Remainder of 2018	12
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization	100	$ 100
Curriculum [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount, beginning balance	160
Adjustments	0
Gross carrying amount, ending balance	160
Accumulated amortization, beginning balance	144
Amortization	4
Accumulated amortization, ending balance	148
Net carrying amount	$ 12
Weighted average amortization period	10 years