ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES - Capital Raising Activities (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended	5 Months Ended	7 Months Ended	12 Months Ended			24 Months Ended
	Feb. 21, 2020	Sep. 30, 2019	Aug. 01, 2017	Feb. 22, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Aug. 11, 2019
Subsidiary, Sale of Stock [Line Items]
Proceeds From Issuance Of Common Stock, net of issuance costs					$ 92,314,000	$ 0	$ 197,607,000
Stock Issued During Period, Value, New Issues					$ 92,314,000		$ 197,607,000
Total shares issued under distribution agreement					14,377,000		20,045,000
At the Market Offering Program [Member]
Subsidiary, Sale of Stock [Line Items]
Proceeds From Issuance Of Common Stock, net of issuance costs	$ 12,200,000		$ 122,900,000	$ 108,200,000				$ 123,100,000
Stock Issued During Period, Value, New Issues	$ 12,400,000		$ 125,000,000	$ 110,000,000				$ 125,000,000
Total shares issued under distribution agreement	2,004,432		12,299,032	10,174,992				15,123,178
At the Market Offering Program [Member] | Maximum [Member]
Subsidiary, Sale of Stock [Line Items]
Stock Issued During Period, Value, New Issues	$ 200,000,000		$ 125,000,000	$ 125,000,000				$ 125,000,000
Follow-on Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Proceeds From Issuance Of Common Stock, net of issuance costs		$ 44,200,000
Stock Issued During Period, Value, New Issues		$ 45,900,000
Total shares issued under distribution agreement		7,000,000