ACQUISITION OF MTGE INVESTMENT CORP - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions			9 Months Ended
	Sep. 07, 2018	Aug. 25, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Business Acquisition [Line Items]
Cash			$ 258,334	$ 0
Preferred Stock, par value (in dollars per share)			$ 0.01		$ 0.01
Series A Preferred Stock
Business Acquisition [Line Items]
Preferred Stock dividend rate, percentage		7.875%
8.125% Series H Cumulative Redeemable Preferred Stock
Business Acquisition [Line Items]
Preferred Stock dividend rate, percentage			8.125%
Mountain Merger Sub Corporation | Series A Preferred Stock
Business Acquisition [Line Items]
Preferred Stock dividend rate, percentage	8.125%
Preferred Stock, par value (in dollars per share)	$ 0.01
Mountain Merger Sub Corporation
Business Acquisition [Line Items]
Total consideration	$ 906,200
Equity issued	455,900
Cash	$ 450,287
Shares issued as part of the consideration for asset acquisition (in shares)	43.6		43.6
Acquisition transaction costs	$ 58,300
Excess consideration for business acquisition	$ 44,500
Mountain Merger Sub Corporation | 8.125% Series H Cumulative Redeemable Preferred Stock
Business Acquisition [Line Items]
Preferred Stock, par value (in dollars per share)	$ 0.01