Real Estate Investments (Real Estate Sales) (Details) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2016 USD ($) mortgage	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of real estate investments, net		$ 6,505	$ 0		$ 0
Payments on mortgage notes payable		19,041	$ 121
Held-for-sale Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract Sales Price		38,000
Gain on sale of real estate investments, net	[1]	$ 6,505
Number of mortgages repaid | mortgage		3
Payments on mortgage notes payable		$ 18,900
Duane Reade | Held-for-sale Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract Sales Price	[2]	12,600
Gain on sale of real estate investments, net	[1],[2]	126
Impairment charge				$ 900
1623 Kings Highway | Held-for-sale Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract Sales Price		17,000
Gain on sale of real estate investments, net	[1]	4,293
Foot Locker | Held-for-sale Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contract Sales Price		8,400
Gain on sale of real estate investments, net	[1]	$ 2,086

[1] Reflected within gain on sale of real estate investments, net in the consolidated statements of operations and comprehensive loss.

[2] Impairment charge of $0.9 million was recognized during the year ended December 31, 2015 in connection with the classification of Duane Reade as held for sale.