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EQUITY AND CASH COMPENSATION UNDER THE PPG AGREEMENTS - Additional Information (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Mar. 31, 2019
Sep. 30, 2018
Jun. 30, 2018
Long-term Purchase Commitment [Line Items]            
Percent of services payable in cash or shares 50.00%   50.00%      
Issuance of common stock in connection with materials and license agreements (in shares) 0 0 0     0
New OLED Materials Agreement and OLED Materials Agreement [Member] | Cash Distribution            
Long-term Purchase Commitment [Line Items]            
Charges to expense (credit) for cash portion of reimbursement of expenses $ 288,000 $ (161,000) $ 362,000     $ 200,000
New OLED Materials Agreement and OLED Materials Agreement [Member] | Weighted Average            
Long-term Purchase Commitment [Line Items]            
Minimum average closing price of common stock (in dollars per share)       $ 20.00 $ 20.00