CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares		6 Months Ended	12 Months Ended
	Apr. 15, 2013	Jun. 30, 2018	Dec. 31, 2017
Preferred Stock, dividend rate		7.50%	7.50%
Preferred Stock | Preferred Stock 7.50% Series B Cumulative Redeemable - Liquidation Preference $25.00 per Share
Preferred Stock, dividend rate	7.50%	7.50%	7.50%
Preferred Stock, liquidation preference per share (in dollars per share)	$ 25.00	$ 25.00	$ 25