SUPPLEMENTAL BALANCE SHEET INFORMATION - Assets Held for Sale, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on impairment and write-off of assets	$ 1,759	$ 2,521	$ 1,075
Flagstaff, AZ | Land
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on impairment and write-off of assets		$ 100