Preferred Stock (Narrative) (Details) - USD ($)					1 Months Ended	12 Months Ended
	Feb. 28, 2017	Apr. 15, 2016	Mar. 16, 2016	Dec. 30, 2005	Feb. 29, 2012	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock [Member]
Class of Stock [Line Items]
Shares issued upon conversion	6,004,957
Shares issued, price per share	$ 10.40
6.25% Convertible Debt [Member]
Class of Stock [Line Items]
Interest rate			6.25%			6.25%
Principal amount			$ 1,012,000
Real Estate Strategies, L.P. [Member]
Class of Stock [Line Items]
Preferred dividends, cash			$ 1,484,000
Percentage of voting stock			49.00%
Real Estate Strategies, L.P. [Member] | 6.25% Convertible Debt [Member]
Class of Stock [Line Items]
Interest rate			6.25%
Principal amount			$ 1,012,000
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate				8.00%		8.00%
Preferred stock, shares issued				1,521,258
Preferred stock, shares outstanding		803,270							803,270
Preferred stock, redemption price		$ 10.00		$ 10.00
Dividends unpaid and accrued per share		$ 2.084940
Redemption liability		$ 9,707,000
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate						10.00%
Preferred stock, redemption price		$ 25.00				$ 25.00
Dividends unpaid and accrued per share		$ 6.354167
Redeemable preferred stock, shares outstanding		332,500							332,500
Redemption liability		$ 10,425,000
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate			6.25%
Preferred dividends, cash							$ 650,000	$ 3,090,000
Preferred stock, shares outstanding								6,245,156
Series D Preferred Stock [Member] | SREP III Flight Investco L.P. [Member]
Class of Stock [Line Items]
Preferred stock, shares issued			3,000,000
Preferred stock, value			$ 30,000,000
Series D Preferred Stock [Member] | Real Estate Strategies, L.P. [Member]
Class of Stock [Line Items]
Preferred stock, shares issued			245,156
Shares issued upon conversion			3,000,000
Series A and B Preferred Stock [Member] | SREP III Flight Investco L.P. [Member]
Class of Stock [Line Items]
Preferred stock, value			$ 20,147,000
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate					6.25%
Preferred stock, shares issued					3,000,000
Percentage of voting stock					34.00%
Series C Preferred Stock [Member] | Real Estate Strategies, L.P. [Member]
Class of Stock [Line Items]
Shares converted			3,000,000
Dividends unpaid and accrued			$ 4,947,000
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, annual dividend rate	6.25%					6.25%
Preferred stock, value						$ 10,050,000	10,050,000
Shares issued upon conversion	925,000
Preferred dividends, cash						$ 578,000	$ 483,000
Preferred stock, shares outstanding	925,000					925,000	925,000
Preferred stock, dividend rate increase resulting from failure to pay dividend, with equity offerings	9.50%