FAIR VALUE MEASUREMENT - Schedule of Unobservable Inputs for Fair Values of Purchase Options (Details) - Recurring basis - Level 3 $ / shares in Thousands	Dec. 31, 2019 $ / shares
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	0.320
Expected volatility | Real Estate Loan 2
Fair value
Purchase options, measurement input	0.380
Expected volatility | Real Estate Loan 3
Fair value
Purchase options, measurement input	0.370
Expected volatility | Real Estate Loan 4
Fair value
Purchase options, measurement input	0.313
Risk free rate | Real Estate Loan 1
Fair value
Purchase options, measurement input	0.017
Risk free rate | Real Estate Loan 2
Fair value
Purchase options, measurement input	0.018
Risk free rate | Real Estate Loan 3
Fair value
Purchase options, measurement input	0.019
Risk free rate | Real Estate Loan 4
Fair value
Purchase options, measurement input	0.015
Expected annualized equity dividend yield | Real Estate Loan 1
Fair value
Purchase options, measurement input	0.068
Expected annualized equity dividend yield | Real Estate Loan 2
Fair value
Purchase options, measurement input	0.099
Expected annualized equity dividend yield | Real Estate Loan 3
Fair value
Purchase options, measurement input	0.065
Expected annualized equity dividend yield | Real Estate Loan 4
Fair value
Purchase options, measurement input	0