STOCKHOLDERS' EQUITY - JonesTrading Agreements (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Class of Stock [Line Items]
Noncash Or Part Noncash Acquisition, Proceeds From Sale Of Common Stock Included In Accounts Receivable				$ 2,848	$ 52,112
Common Stock, Aggregate Offering Price	$ 150,000
Additional paid-in capital
Class of Stock [Line Items]
Noncash Or Part Noncash Acquisition, Proceeds From Sale Of Common Stock Included In Accounts Receivable		$ 0	$ 12,198	$ 0	$ 52,112
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