CAPITAL STOCK - Completed public offerings ofcommon stock (Details) - USD ($)	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Stock Issued During Period, Value, New Issues				$ 197,607,000	$ 118,328,000
At the Market Offering Program [Member]
Book Value Per Share	$ 8.71	$ 9.23	$ 9.75	$ 8.71	$ 10.1	$ 9.15
Weighted Average Price Received Per Share	$ 9.81	$ 10.17	$ 10.13	$ 9.81
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	$ 74,750,000	$ 110,065,000	$ 12,792,000	$ 197,607,000