Investment in 111 West 57th Partners LLC (Details) $ in Thousands		3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 29, 2017 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2014	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)	May 31, 2016 USD ($)	Jun. 28, 2013 USD ($) ft²
Schedule of Equity Method Investments [Line Items]
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
Annaly CRE LLC initial mortgage and acquisition loan repaid		$ 230,000
Impairment of equity investment in 111 West 57th Partners LLC					$ 63,745	$ 0
Assets [Abstract]
Real estate held for development, net						563,133
Escrow deposits						9,000
Other assets						6,908
Total assets						579,041
Liabilities [Abstract]
Loans payable						441,749
Other liabilities						16,788
Total liabilities						458,537
Equity [Abstract]
Total members' equity						120,504
Total liabilities and members' equity						579,041
Income (Loss) [Abstract]
Rental income				$ 0		0
Expenses				25		953
Net income (loss)				$ (25)		$ (953)
Line of Credit [Member] | R. A. Bianco [Member]
Schedule of Equity Method Investments [Line Items]
Maximum borrowing capacity							$ 10,000	$ 1,000
Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Additional borrowing required to complete project					60,000
Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Additional borrowing required to complete project					$ 100,000
Capital LLC [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of outstanding shares to be owned by CEO					20.00%
Investment LLC [Member] | Capital LLC [Member]
Schedule of Equity Method Investments [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.
AIG [Member]
Schedule of Equity Method Investments [Line Items]
Financing obtained by 111 W 57th Partners		400,000
Apollo [Member]
Schedule of Equity Method Investments [Line Items]
Financing obtained by 111 W 57th Partners		$ 325,000
Junior Mezzanine Loan [Member]
Schedule of Equity Method Investments [Line Items]
Junior mezzanine loan sold by lender to an affiliate of Spruce Capital Partners LLC	$ 25,000