Investment in 111 West 57th Partners LLC (Details) $ in Thousands		3 Months Ended	9 Months Ended
	Jun. 30, 2015 USD ($)	Mar. 31, 2014	Sep. 30, 2018 USD ($)	Mar. 31, 2017 USD ($)	May 31, 2016 USD ($)	Jun. 28, 2013 USD ($) ft²
Initial Investment and Other Information Relating to the 111 West 57th Property [Abstract]
Company's aggregate initial investment						$ 57,250
Company's aggregate initial membership interest %						60.30%
Other members and Sponsor initial investment						$ 37,750
Approximate gross square feet of project | ft²						346,000
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%
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%
Term of loan			4 years
Extension option of loan			1 year
Information Relating to Financing for 111 West 57th Partners [Abstract]
Annaly CRE LLC initial mortgage and acquisition loan repaid	$ 230,000
Line of Credit [Member] | R. A. Bianco [Member]
Information Relating to Financing for 111 West 57th Partners [Abstract]
Maximum borrowing capacity				$ 10,000	$ 1,000
Minimum [Member]
Information Relating to Financing for 111 West 57th Partners [Abstract]
Additional borrowing required to complete project			$ 60,000
Maximum [Member]
Information Relating to Financing for 111 West 57th Partners [Abstract]
Additional borrowing required to complete project			$ 100,000
Capital LLC [Member]
Initial Investment and Other Information Relating to the 111 West 57th Property [Abstract]
Percentage of outstanding shares to be owned by CEO			20.00%
Investment LLC [Member] | Capital LLC [Member]
Initial Investment and Other Information Relating to the 111 West 57th Property [Abstract]
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.
AIG [Member]
Information Relating to Financing for 111 West 57th Partners [Abstract]
Financing obtained by 111 W 57th Partners	400,000
Apollo [Member]
Information Relating to Financing for 111 West 57th Partners [Abstract]
Financing obtained by 111 W 57th Partners	$ 325,000