SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2015 Transaction	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Accounts Receivable
Income Property Tenant Receivables		$ 1,934	$ 2,330
Number of closed land transactions | Transaction	2
Allowance for doubtful accounts		600	500
Other Assets
Accounts Receivable
Income Property Tenant Receivables		1,900	2,300
Accounts receivable related to real estate operations		$ 1,300	$ 1,300