Preferred Equity Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Preferred equity ownership percentage	24.40%
Preferred equity investments, gross	$ 55,458	$ 55,405
Less: valuation allowance	(19,588)	(19,588)
Total preferred equity investments, net	$ 35,870	35,817
470 Vanderbilt Avenue [Member]
Investment Holdings [Line Items]
Preferred equity ownership percentage	24.40%
Preferred Equity Investments, Dividend Rate	10.30%
Preferred Equity Investments, Initial Maturity	2019-02
Preferred equity investments, gross	$ 35,870	35,817
2 Herald Square [Member]
Investment Holdings [Line Items]
Preferred equity ownership percentage	24.40%
Preferred Equity Investments, Dividend Rate	10.30%
Preferred Equity Investments, Initial Maturity	2017-04
Preferred equity investments, gross	$ 19,588	$ 19,588