Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Real estate, accumulated depreciation	$ 30,555	$ 28,768
Investments in real estate, net of accumulated depreciation	235,148	245,904
Intangible assets, accumulated amortization	7,258	6,831
Indebtedness, unamortized discounts, premiums and deferred financing costs	26,205	29,465
Indebtedness, net of unamortized discounts, premiums and deferred financing costs	$ 1,272,006	$ 1,390,188
Preferred shares, authorized	25,000,000	25,000,000
Common shares, par value	$ 0.03	$ 0.03
Common shares, shares authorized	200,000,000	200,000,000
Common shares, shares issued	92,576,726	93,045,152
Common shares, shares outstanding	92,576,726	93,045,152
Unvested restricted common share awards	619,328	1,246,484
VIE
Investment in mortgage loans	$ 1,022,997	$ 1,174,827
Real estate, accumulated depreciation	7,175	6,902
Investments in real estate, net of accumulated depreciation	18,395	18,634
Indebtedness, net of unamortized discounts, premiums and deferred financing costs	$ 951,243	$ 1,038,864
Series D Cumulative Redeemable Preferred Stock
Series D cumulative redeemable preferred shares, par value	$ 0.01	$ 0.01
Series D cumulative redeemable preferred shares, shares authorized	4,000,000	4,000,000
Series D cumulative redeemable preferred shares, shares issued	2,939,190	3,133,720
Series D cumulative redeemable preferred shares, shares outstanding	2,939,190	3,133,720
7.75% Series A Cumulative Redeemable Preferred Stock
Preferred shares, authorized	8,069,288	8,069,288
Preferred shares, dividend rate	7.75%	7.75%
Cumulative redeemable preferred shares, liquidation preference	$ 25.00	$ 25.00
Cumulative redeemable preferred shares, shares issued	5,344,353	5,344,353
Cumulative redeemable preferred shares, shares outstanding	5,344,353	5,344,353
Preferred shares, par value	$ 0.01	$ 0.01
8.375% Series B Cumulative Redeemable Preferred Stock
Preferred shares, authorized	4,300,000	4,300,000
Preferred shares, dividend rate	8.375%	8.375%
Cumulative redeemable preferred shares, liquidation preference	$ 25.00	$ 25.00
Cumulative redeemable preferred shares, shares issued	2,340,969	2,340,969
Cumulative redeemable preferred shares, shares outstanding	2,340,969	2,340,969
Preferred shares, par value	$ 0.01	$ 0.01
8.875% Series C Cumulative Redeemable Preferred Stock
Preferred shares, authorized	3,600,000	3,600,000
Preferred shares, dividend rate	8.875%	8.875%
Cumulative redeemable preferred shares, liquidation preference	$ 25.00	$ 25.00
Cumulative redeemable preferred shares, shares issued	1,640,425	1,640,425
Cumulative redeemable preferred shares, shares outstanding	1,640,425	1,640,425
Preferred shares, par value	$ 0.01	$ 0.01
Series E Cumulative Redeemable Preferred Stock
Preferred shares, authorized	4,000,000	4,000,000
Preferred shares, par value	$ 0.01	$ 0.01