CAPITAL STOCK - Completed public offerings ofcommon stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Stock Issued During Period, Value, New Issues	$ 0
At the Market Offering Program [Member]
Book Value Per Share		$ 8.71	$ 9.23	$ 9.75	$ 8.71	$ 9.15	$ 10.1
Weighted Average Price Received Per Share		$ 9.81	$ 10.17	$ 10.13	$ 9.81			$ 10.17
Stock Issued During Period Shares New Issues		7,746,052	11,012,836	1,286,196	20,045,084
Stock Issued During Period, Value, New Issues		$ 74,750	$ 110,065	$ 12,792	$ 197,607