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INVESTMENTS HELD-TO-MATURITY (Details) - USD ($)
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]      
Amortized cost $ 6,500,000    
Fair value 0    
Unrealized Gain (Loss) 0    
Investments held-to-maturity 6,477,000   $ 16,863,000
Interest and investment income 106,000 $ 48,000  
Commercial Paper | Commercial Paper, Maturing April 2019      
Schedule of Held-to-maturity Securities [Line Items]      
Investments held-to-maturity 2,500,000    
Commercial Paper | Commercial Paper, Maturing May 2019      
Schedule of Held-to-maturity Securities [Line Items]      
Investments held-to-maturity 1,500,000    
Commercial Paper | Commercial Paper, Maturing June 2019      
Schedule of Held-to-maturity Securities [Line Items]      
Investments held-to-maturity 1,500,000    
Commercial Paper | Commercial Paper, Maturing August 2019      
Schedule of Held-to-maturity Securities [Line Items]      
Investments held-to-maturity $ 1,000,000