Investment in 111 West 57th Partners LLC (Details)		1 Months Ended	3 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($)	Jul. 31, 2015 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2014	Dec. 31, 2016 USD ($)	May 31, 2016 USD ($)	Jun. 28, 2013 USD ($) ft²
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
Term of loan			4 years
Extension option of loan			1 year
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
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%
Capital contributed by Capital LLC		$ 9,868,000
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
Assets [Abstract]
Real estate held for development, net			598,064,000		$ 563,133,000
Escrow deposits			9,250,000		9,000,000
Other assets			5,790,000		6,908,000
Total assets			613,104,000		579,041,000
Liabilities [Abstract]
Loans payable			475,122,000		441,749,000
Other liabilities			17,509,000		16,788,000
Total liabilities			492,631,000		458,537,000
Equity [Abstract]
Total members' equity			120,473,000		120,504,000
Total liabilities and members' equity			613,104,000		579,041,000
Income (Loss) [Abstract]
Rental income			0		0
Expenses			31,000		650,000
Net income (loss)			$ (31,000)		$ (650,000)
Capital LLC [Member]
Noncontrolling Interest [Line Items]
Percentage of outstanding shares to be owned by CEO			20.00%
Line of Credit [Member] | R. A. Bianco [Member]
Subsequent Event [Line Items]
Maximum borrowing capacity			$ 10,000,000			$ 1,000,000
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.