EQUITY OFFERING - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Jun. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Proceeds from issuance of common stock net of offering expense	$ 381,100
Proceeds from issuance of common stock net of offering expenses		$ 398,600	$ 381,261	$ 399,600	$ 23,053
Common Stock
Class of Stock [Line Items]
Shares issued for stock offering (in shares)	18,170,000		18,170,000	5,700,000
Shares issued (in shares)		5,700,000