Preferred Equity Investments (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Preferred equity ownership percentage	24.40%
Preferred equity investments, gross	$ 55,351	$ 55,051
Less: valuation allowance	(19,588)	0
Preferred equity investments, net	$ 35,763	55,051
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	$ 35,763	35,613
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	$ 19,438