Investment in 111 West 57th Partners LLC (Details)		3 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($)	Mar. 31, 2016 USD ($) ft²	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jul. 31, 2015 USD ($)
Investment in 111 West 57th Partners LLC [Abstract]
Company's aggregate initial investment		$ 57,250,000
Company's aggregate initial membership interest percentage		60.30%
Other members and Sponsor initial investment		$ 37,750,000
Approximate gross square feet of project | ft²		346,000
Financing obtained by 111 W 57th Partners	$ 725,000,000
Annaly CRE LLC initial mortgage and acquisition loan repaid	$ 230,000,000
Distribution attributable to Company's investment						$ 11,699,000
Distribution retained by the Company, net of amounts repaid to Capital LLC						$ 1,831,000
Capital contributed by Capital LLC					$ 9,868,000
Term of loan	4 years
Extension option of loan	1 year
Description of partnership agreement distribution		The JV Agreement and related operating agreements generally provide that all distributable cash shall be distributed as follows: (i) first, 100% to the members in proportion to their percentage interests until Investment LLC has received distributions yielding a 20% internal rate of return as calculated; (ii) second, 100% to the Sponsor as a return of (but not a return on) any additional capital contributions made by the Sponsor on account of manager overruns; and (iii) thereafter, (a) 50% to the members in proportion to their respective percentage interests at the time of such distribution, and (b) 50% to the Sponsor.
Subordinated participation interest to CEO		10.00%
Percentage of distribution on company's initial investment to be received prior to CEO receiving percentage distribution		150.00%
Percentage of outstanding shares to be owned by CEO, minimum		20.00%
Noncontrolling Interest [Line Items]
Capital contributions		$ 0
Valuation of shortfall capital contribution as multiple of amount actually contributed		1.5
Sponsor calculation of investment LLC aggregate investment percentage after dilution		48.00%
Difference between the Company's carrying amount and the underlying equity		$ 867,000
Impairment on the Company's equity method investments		0		$ 0
Assets [Abstract]
Real estate held for development, net		468,219,000		440,370,000
Escrow deposits		9,400,000		9,400,000
Other assets		22,708,000		26,827,000
Total assets		500,327,000		476,597,000
Liabilities: [Abstract]
Loans payable		365,180,000		340,693,000
Other liabilities		14,340,000		14,447,000
Total liabilities		379,520,000		355,140,000
Equity: [Abstract]
Total members' equity		120,807,000		121,457,000
Total liabilities and members' equity		500,327,000		$ 476,597,000
Income (Loss) [Abstract]
Rental income		0	$ 0
Expenses		650,000	417,000
Net income (loss)		$ (650,000)	$ (417,000)
Investment LLC [Member] | Capital LLC [Member]
Noncontrolling Interest [Line Items]
Terms of distributions to Capital LLC				available cash of Investment LLC will be distributed first to Capital LLC until it has received a 20% internal rate of return (calculated as provided for in the JV Agreement as noted above), second to the Company until it has received 150% of its capital, and; thereafter, available cash is split 10/90 with 10% going to Mr. R.A. Bianco as the subordinated participation interest noted above and 90% going to Capital LLC and the Company pari-passu, with Capital LLC receiving one-half of its pro-rata share based on capital contributed and the Company receiving the balance.