FAIR VALUE MEASUREMENT - Schedule of Unobservable Inputs for Fair Values of Purchase Options (Details) - Recurring basis - Level 3 $ / shares in Thousands	12 Months Ended
	Dec. 31, 2020 $ / shares
Real Estate Loan 1
Fair value
Purchase options, term	2 years 7 months 2 days
Real Estate Loan 2
Fair value
Purchase options, term	2 years 8 months 4 days
Real Estate Loan 3
Fair value
Purchase options, term	2 years 8 months 1 day
Real Estate Loan 4
Fair value
Purchase options, term	1 year 5 months 1 day
Exercise price | Real Estate Loan 1
Fair value
Purchase options, measurement input	15,143
Exercise price | Real Estate Loan 2
Fair value
Purchase options, measurement input	17,377
Exercise price | Real Estate Loan 3
Fair value
Purchase options, measurement input	5,503
Exercise price | Real Estate Loan 4
Fair value
Purchase options, measurement input	37,800
Expected volatility | Real Estate Loan 1
Fair value
Purchase options, measurement input	0.650
Expected volatility | Real Estate Loan 2
Fair value
Purchase options, measurement input	0.550
Expected volatility | Real Estate Loan 3
Fair value
Purchase options, measurement input	0.550
Expected volatility | Real Estate Loan 4
Fair value
Purchase options, measurement input	0.550
Risk-free rate | Real Estate Loan 1
Fair value
Purchase options, measurement input	0.003
Risk-free rate | Real Estate Loan 2
Fair value
Purchase options, measurement input	0.003
Risk-free rate | Real Estate Loan 3
Fair value
Purchase options, measurement input	0.003
Risk-free rate | Real Estate Loan 4
Fair value
Purchase options, measurement input	0.002
Expected annualized equity dividend yield | Real Estate Loan 1
Fair value
Purchase options, measurement input	0.065
Expected annualized equity dividend yield | Real Estate Loan 2
Fair value
Purchase options, measurement input	0.075
Expected annualized equity dividend yield | Real Estate Loan 3
Fair value
Purchase options, measurement input	0.171
Expected annualized equity dividend yield | Real Estate Loan 4
Fair value
Purchase options, measurement input	0