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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Notes Receivable and Allowance for Doubtful Accounts (Details)
Mar. 31, 2018
USD ($)
item
Dec. 31, 2017
USD ($)
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES    
Number of notes receivable | item 1  
Allowance for doubtful accounts | $ $ 250,000 $ 250,000