FAIR VALUE MEASUREMENTS - Changes in Fair Value of Receivables (Details) - Fair Value, Recurring - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages and notes receivable	$ 48,364	$ 24,315	$ 30,994
Change in fair value of receivables	1,770	263
Other Gains (Losses)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of receivables	11	3
Interest Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of receivables	$ 1,759	$ 260