ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES - Capital Raising Activities (Narrative) (Details) - USD ($)	2 Months Ended		5 Months Ended	7 Months Ended	9 Months Ended
	Sep. 30, 2017	Feb. 20, 2013	Aug. 01, 2017	Feb. 22, 2017	Sep. 30, 2017	Sep. 30, 2016
Subsidiary, Sale of Stock [Line Items]
Proceeds From Issuance Of Common Stock, net of issuance costs					$ 122,857,000	$ 47,116,000
Stock Issued During Period, Value, New Issues					$ 122,857,000
Initial Public Offering [Member]
Subsidiary, Sale of Stock [Line Items]
Stock Issued During Period, Value, New Issues		$ 35,400,000
Total shares issued under distribution agreement		2,400,000
At the Market Offering Program [Member]
Subsidiary, Sale of Stock [Line Items]
Proceeds From Issuance Of Common Stock, net of issuance costs	$ 0		$ 122,900,000	$ 108,200,000
Stock Issued During Period, Value, New Issues	$ 0		$ 125,000,000	$ 110,000,000
Total shares issued under distribution agreement	0		12,299,032	10,174,992
At the Market Offering Program [Member] | Maximum [Member]
Subsidiary, Sale of Stock [Line Items]
Stock Issued During Period, Value, New Issues	$ 125,000,000		$ 125,000,000	$ 125,000,000