EQUITY AND CASH COMPENSATION UNDER THE PPG AGREEMENTS - Additional Information (Details) - USD ($)	6 Months Ended		12 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long-term Purchase Commitment [Line Items]
Percent of services payable in cash or shares			50.00%
Issuance of common stock in connection with materials and license agreements (in shares)			0	0	0
New OLED Materials Agreement and OLED Materials Agreement [Member] | Cash Distribution
Long-term Purchase Commitment [Line Items]
Charges to expense for cash portion of reimbursement of expenses			$ 771,000	$ 1,700,000	$ 2,300,000
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