CAPITAL STOCK - Completed public offerings ofcommon stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended							9 Months Ended	12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Dec. 31, 2016
Stock Issued During Period, Value, New Issues								$ 122,857
At the Market Offering Program [Member]
Weighted Average Price Received Per Share	$ 0	$ 10.17	$ 10.13	$ 10.79	$ 10.8	$ 10.48	$ 0	$ 0	$ 10.79
Stock Issued During Period Shares New Issues	0	11,012,836	1,286,196	6,707,101	3,818,802	646,753	0	12,299,032	11,172,656
Stock Issued During Period, Value, New Issues	$ 0	$ 110,065	$ 12,792	$ 71,212	$ 40,525	$ 6,591	$ 0	$ 122,857	$ 118,328