Mortgages Payable (Details Textual) - USD ($) $ in Thousands		1 Months Ended				12 Months Ended
		Aug. 28, 2018	Jul. 31, 2018	Apr. 26, 2018	Dec. 16, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 29, 2018	Jun. 30, 2018
Line of Credit Facility [Line Items]
Real Estate Investments, Net						$ 1,693,757	$ 1,397,582
Debt Instrument, Basis Spread on Variable Rate						1.75%
Extinguishment of Debt, Amount					$ 38,100
Amortization of Debt Issuance Costs						$ 4,300	2,500	$ 1,300
Amortisation Of Fair Value Adjustments Of Debt						$ 400	300	$ 400
Mortgages [Member]
Line of Credit Facility [Line Items]
Debt Instrument Prepayment Fee Percentage						2.35%
Secured Debt	[1]					$ 1,215,376	946,101
Enders Place at Baldwin Park [Member]
Line of Credit Facility [Line Items]
Secured Long-term Debt, Noncurrent						$ 16,200
Debt Instrument, Basis Spread on Variable Rate						3.97%
Enders Place at Baldwin Park [Member] | Supplemental Loan [Member]
Line of Credit Facility [Line Items]
Secured Long-term Debt, Noncurrent						$ 7,600
Debt Instrument, Basis Spread on Variable Rate						5.01%
Park Kingston [Member]
Line of Credit Facility [Line Items]
Secured Long-term Debt, Noncurrent						$ 15,300
Debt Instrument, Basis Spread on Variable Rate						3.21%
Park Kingston [Member] | Supplemental Loan [Member]
Line of Credit Facility [Line Items]
Secured Long-term Debt, Noncurrent						$ 3,200
Debt Instrument, Basis Spread on Variable Rate						4.34%
ARIUM Gulfshore [Member]
Line of Credit Facility [Line Items]
Secured Debt				$ 32,600
Extinguishment of Debt, Amount				300
ARIUM at Palmer Ranch [Member]
Line of Credit Facility [Line Items]
Secured Debt				$ 41,300			$ 26,900
Arium Glenridge [Member]
Line of Credit Facility [Line Items]
Secured Debt		$ 49,500								$ 48,400
Extinguishment of Debt, Amount		$ 500
Arium Palms [Member]
Line of Credit Facility [Line Items]
Secured Debt									$ 30,300	25,000
Ashton Reserve II [Member]
Line of Credit Facility [Line Items]
Secured Debt			$ 15,200							15,300
Extinguishment of Debt, Amount			200
Preston View Mortgage [Member]
Line of Credit Facility [Line Items]
Secured Debt			41,700							$ 41,100
Extinguishment of Debt, Amount			$ 400

[1] All the Company’s floating rate mortgages bear interest at one-month LIBOR + margin. In December 2018, one-month LIBOR in effect was 2.35%. LIBOR rate is subject to a rate cap. Please refer to Note 11 for further information.