Loans Payable and Secured Line of Credit - Additional Information (Details)		1 Months Ended		6 Months Ended	12 Months Ended
	Apr. 05, 2020 USD ($)	Jun. 30, 2020 USD ($)	May 31, 2018 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) item	Dec. 31, 2017 USD ($) ft²	Apr. 06, 2020 USD ($)
Line of Credit Facility, Maximum Borrowing Capacity					$ 70,000,000
Loans Payable		$ 177,329,000		$ 177,329,000	$ 169,735,000
Liquidity Requirement	$ 10,000,000.0						$ 15,000,000.0
Sterling National Bank [Member]
Line of Credit Facility, Maximum Borrowing Capacity		12,750,000		$ 12,750,000
Debt Instrument, Interest Rate Terms				200 basis points over the 30-day LIBOR
Landmarked Robert And Anne Dickey House [Member]
Area of Real Estate Property | ft²						7,500
Loans Payable [Member]
Debt Instrument, Interest Rate Terms			bearing interest at a blended average rate of 3.72% over the 30-day LIBOR, each with a one year extension option upon satisfaction of certain conditions
Delayed draw facility		4,250,000		$ 4,250,000
Remediation reserves		3,600,000		3,600,000
Interest reserve		$ 800,000		$ 800,000
Debt Instrument, Interest Rate, Increase (Decrease)		25.00%
Exit fee (as a percent)		1.00%		1.00%
Debt Instrument Blended Effective Interest Rate					5.48%
Debt Instrument, Face Amount			$ 67,800,000
Debt Instrument, Payment Terms		a guaranty of 25% of the principal amount, decreasing to 10% of the principal balance upon the debt yield ratio becoming equal to or greater than 7.0%.
Debt Instrument, Interest Rate, Effective Percentage		2.25%		2.25%
Debt Instrument Exit Fee Rate, Increase (Decrease)		50.00%
Loans Payable [Member] | Canadian Imperial Bank of Commerce [Member]
Debt Instrument, Face Amount			52,400,000
Debt, Weighted Average Interest Rate		0.50%		0.50%
Mezzanine Loan [Member] | RCG LV Debt VI REIT LLC [Member]
Debt Instrument, Face Amount			$ 15,400,000
Letter of Credit [Member]
Loans Payable		$ 7,250,000		$ 7,250,000	$ 5,250,000
Debt Instrument, Interest Rate, Effective Percentage		2.16%		2.16%	3.76%
Minimum [Member] | Loans Payable [Member]
Interest rate basis (as a percent)		50.00%
Maximum [Member]
Debt Instrument, Interest Rate, Stated Percentage						2.50%
Maximum [Member] | Loans Payable [Member]
Interest rate basis (as a percent)		2.75%
Corporate Loan [Member]
Line of Credit Facility, Maximum Borrowing Capacity					$ 70,000,000.0
Increase in maximum borrowing capacity					$ 25,000,000.0
Term of the debt					32 months
Loans Payable		$ 34,000,000.0		$ 34,000,000.0
Debt Instrument, Interest Rate Terms					a rate per annum equal to the sum of (i) 5.25% (the “PIK Interest Rate”) and (ii) a scheduled interest rate (the “Cash Pay Interest Rate”) based on six-month periods from the Closing Date, which Cash Pay Interest Rate, from the Closing Date until the six-month anniversary of the Closing Date, equals 4.0%, subject to increase during the extension periods.
Debt Instrument, Interest Rate, Basis for Effective Rate				9.375%
Commitment fee		1,800,000		$ 1,800,000	$ 2,450,000
Commitment fee, payable on the initial draw (as a percent)					50.00%
Commitment fee, payable on subsequent draws (as a percent)					50.00%
Exit fee (as a percent)					1.00%
Multiple On Invested Capital (as a percent)					130.00%
Collateral for loan, equity interests in subsidiaries (as a percent)					100.00%
Common stock repurchase through proceeds from debt, amount authorized					$ 2,000,000.0
Common stock repurchase through other sources of cash, amount authorized					$ 1,500,000
Threshold minimum loan outstanding (as a percent)					50.00%
Number of board members who can be appointed by the lender | item					1
Maximum number of committees of the board, that the Designee can sit | item					3
Corporate Loan [Member] | Greenwich Ny 77 [Member]
Net cash proceeds of residential condominium sales (as a percent)					70.00%
Corporate Loan [Member] | Minimum [Member]
Net cash proceeds of residential condominium sales (as a percent)					90.00%
Corporate Loan [Member] | Maximum [Member]
Net cash proceeds of residential condominium sales (as a percent)					100.00%
Corporate Loan [Member] | PIK Interest Rate
Interest rate basis (as a percent)					5.25%
Corporate Loan [Member] | Cash Pay Interest Rate
Interest rate basis (as a percent)					4.00%
Greenwich Construction Loan [Member]
Term of the debt				4 years
Loans Payable		$ 126,900,000		$ 126,900,000	$ 104,900,000
Debt Instrument, Face Amount						$ 189,500,000
Debt Instrument, Interest Rate, Effective Percentage		9.25%		9.25%	10.01%
Number of Real Estate Properties						90
Debt Instrument, Description						LIBOR plus 8.25% and (ii) 9.25%.
Liquidity Requirement	$ 15,000,000.0						$ 10,000,000.0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments				$ 0
Maximum Unrestricted Cash on Liquidity Percent	50.00%
Debt Instrument, Unamortized Premium						$ 393,000
Derivative, Notional Amount						$ 189,500,000
Greenwich Construction Loan [Member] | Interest Rate Cap [Member] | Not Designated as Hedging Instrument [Member]
Derivative Asset		$ 0		0	$ 0
Greenwich Construction Loan [Member] | Letter of Credit [Member]
Loans Payable		$ 3,580,000		$ 3,580,000