Loans Payable and Secured Line of Credit - Additional Information (Details)			1 Months Ended			9 Months Ended		12 Months Ended
	May 07, 2019 USD ($)	May 11, 2016 USD ($)	May 31, 2018 USD ($)	Dec. 22, 2017 USD ($) ft²	Feb. 22, 2017 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Aug. 04, 2017 USD ($)
Interest Costs Capitalized						$ 495,000
Interest Expense, Debt								$ 1,000
Long-term Line of Credit						5,037,000		0
Line of Credit Facility, Expiration Date					Feb. 22, 2019
Loans Payable						167,346,000		123,333,000
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.
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%.
Cash and Cash Equivalents, at Carrying Value						5,705,000	$ 14,620,000	$ 11,496,000	$ 15,273,000
Proceeds from Issuance of Debt						$ 42,448,000	$ 78,263,000
Maximum [Member]
Debt Instrument, Interest Rate, Stated Percentage		3.00%		2.50%
Loans Payable [Member]
Debt Instrument, Interest Rate, Effective Percentage						5.74%		6.22%
Debt Instrument, Face Amount			$ 67,800,000
Letter of Credit [Member]
Debt Instrument, Interest Rate, Effective Percentage						4.02%
Loans Payable						$ 5,000,000
Landmarked Robert And Anne Dickey House [Member]
Area of Real Estate Property | ft²				7,500
Sterling National Bank [Member]
Debt Instrument, Description of Variable Rate Basis					100			200
Line of Credit Facility, Maximum Borrowing Capacity					$ 12,000,000			$ 12,750,000		$ 11,000,000
Secured Debt											$ 2,900,000
Line of Credit Facility, Remaining Borrowing Capacity										$ 9,100,000
Interest Rate Cap [Member]
Interest Expense, Debt						1,000
Interest Rate Cap [Member] | Prepaid Expenses and Other Current Assets [Member]
Derivative Asset, Fair Value, Gross Asset						$ 2,000		$ 497,000
West Palm Beach Florida Loan [Member]
Debt Instrument, Interest Rate, Basis for Effective Rate		interest at 30-day LIBOR plus 230 basis points.
Debt Instrument, Interest Rate, Effective Percentage						4.32%		4.80%
Debt Instrument, Unamortized Premium		$ 14,000
Line of Credit Facility, Maximum Borrowing Capacity		12,600,000
Derivative, Notional Amount		9,100,000
Line of Credit Facility, Remaining Borrowing Capacity						$ 2,300,000
Proceeds from Issuance of Debt	$ 1,200,000
Available Of Capital Lease Commitment Reimbursement	$ 3,500,000
West Palm Beach Florida Loan [Member] | Interest Rate Cap [Member] | Prepaid Expenses and Other Current Assets [Member]
Derivative Asset, Fair Value, Gross Asset						$ 1,000
Greenwich Construction Loan [Member]
Debt Instrument, Interest Rate, Effective Percentage						10.27%		10.60%
Debt Instrument, Unamortized Premium				$ 393,000
Derivative, Notional Amount				189,500,000
Debt Instrument, Face Amount				$ 189,500,000
Number of Real Estate Properties				90
Debt Instrument, Description				LIBOR plus 8.25% and (ii) 9.25%.
Loans Payable						$ 92,800,000		$ 51,500,000
Cash and Cash Equivalents, at Carrying Value				$ 15,000,000		10,000,000
Greenwich Construction Loan [Member] | Letter of Credit [Member]
Loans Payable						7,000,000		7,000,000
Greenwich Construction Loan [Member] | Multi Use Building [Member]
Area of Real Estate Property | ft²				300,000
TPH Borrower [Member] | West Palm Beach Florida Loan [Member]
Long-term Line of Credit		9,100,000				$ 10,300,000
Derivative, Notional Amount		$ 9,100,000						$ 9,100,000
Canadian Imperial Bank of Commerce [Member] | Loans Payable [Member]
Debt Instrument, Face Amount			52,400,000
Debt, Weighted Average Interest Rate						0.50%
RCG LV Debt VI REIT LLC [Member] | Mezzanine Loan [Member]
Debt Instrument, Face Amount			$ 15,400,000