NATURE OF OPERATIONS AND LIQUIDITY - Additional Information (Details)	3 Months Ended
Mar. 31, 2019 USD ($) License	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Nature Of Operations And Liquidity [Line Items]
Accumulated deficit	$ 230,379,928		$ 214,552,728
Net cash used in operating activities	9,600,592	$ 10,931,732
Cash, cash equivalents, restricted cash and marketable securities	$ 79,300,000
Development-stage Proprietary Compounds
Nature Of Operations And Liquidity [Line Items]
Number of licenses acquired \| License	4

Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3536-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3521-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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