STOCKHOLDERS' EQUITY - JonesTrading Agreements (Details) - USD ($) $ in Thousands		3 Months Ended
	Apr. 09, 2020	Mar. 31, 2020	Mar. 31, 2019
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock		$ 2,848	$ 30,957
Additional paid-in capital
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock		$ 0	$ 39,914
Subsequent Event [Member]
Class of Stock [Line Items]
Common Stock, Aggregate Offering Price	$ 80,000
At-The-Market Agreement [Member] | JonesTrading Institutional Services LLC [Member]
Class of Stock [Line Items]
Sale of Stock, Number of Shares Issued in Transaction		415,904