Mortgages Payable (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Fair value adjustments		$ 2,204	$ 2,638
Deferred financing costs, net		(11,444)	(9,245)
Total		1,206,136	939,494
Mortgages [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	1,215,376	946,101
ARIUM at Palmer Ranch [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 41,348	26,925
Interest Rate		4.41%
Interest Only Through Date		May 2020
Maturity Date		May 01, 2025
ARIUM Glenridge [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 49,500	48,431
Interest Rate	[1]	3.68%
Interest Only Through Date	[1]	September 2021
Maturity Date	[1]	Sep. 01, 2025
ARIUM Grandewood [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[2]	$ 19,713	0
Interest Rate	[2]	4.35%
Interest Only Through Date	[2]	July 2020
Maturity Date	[2]	Jul. 01, 2025
ARIUM Grandewood [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1],[2]	$ 19,672	34,294
Interest Rate	[1],[2]	3.75%
Interest Only Through Date	[1],[2]	July 2020
Maturity Date	[1],[2]	Jul. 01, 2025
ARIUM Gulfshore [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 0	32,626
Interest Rate		0.00%
ARIUM Hunters Creek [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 72,294	72,294
Interest Rate		3.65%
Interest Only Through Date		November 2019
Maturity Date		Nov. 01, 2024
ARIUM Metrowest [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 64,559	0
Interest Rate		4.43%
Interest Only Through Date		May 2021
Maturity Date		May 01, 2025
ARIUM Palms [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 30,320	24,999
Interest Rate	[1]	3.75%
Interest Only Through Date	[1]	September 2020
Maturity Date	[1]	Sep. 01, 2025
ARIUM Pine Lakes [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 26,950	26,950
Interest Rate		3.95%
Interest Only Through Date		Interest-only
Maturity Date		Nov. 01, 2023
ARIUM Westside [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 52,150	52,150
Interest Rate		3.68%
Interest Only Through Date		August 2021
Maturity Date		Aug. 01, 2023
Ashford Belmar [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 100,675	0
Interest Rate		4.53%
Interest Only Through Date		December 2022
Maturity Date		Dec. 01, 2025
Ashton Reserve I [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 30,878	31,401
Interest Rate		4.67%
Interest Only Through Date	[3]
Maturity Date		Dec. 01, 2025
Ashton Reserve II [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 15,213	15,270
Interest Rate	[1]	3.85%
Interest Only Through Date	[1]	August 2022
Maturity Date	[1]	Aug. 01, 2025
Citrus Tower [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 41,438	41,438
Interest Rate		4.07%
Interest Only Through Date		October 2019
Maturity Date		Oct. 01, 2024
Enders Place at Baldwin Park [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[4]	$ 23,822	24,287
Interest Rate	[4]	4.30%
Interest Only Through Date	[3],[4]
Maturity Date	[4]	Nov. 01, 2022
James on South First [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 26,500	26,500
Interest Rate		4.35%
Interest Only Through Date		January 2019
Maturity Date		Jan. 01, 2024
Marquis at Crown Ridge [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 28,634	29,217
Interest Rate	[1]	3.96%
Interest Only Through Date	[1],[3]
Maturity Date	[1],[5]	Jun. 01, 2024
Marquis at Stone Oak [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 42,725	43,125
Interest Rate	[1]	3.96%
Interest Only Through Date	[1],[3]
Maturity Date	[1],[5]	Jun. 01, 2024
Marquis at the Cascades I [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 32,899	33,207
Interest Rate	[1]	3.96%
Interest Only Through Date	[1],[3]
Maturity Date	[1],[5]	Jun. 01, 2024
Marquis at Cascades II [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 22,960	23,175
Interest Rate	[1]	3.96%
Interest Only Through Date	[1],[3]
Maturity Date	[1],[5]	Jun. 01, 2024
Marquis at TPC [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 16,826	17,184
Interest Rate	[1]	3.96%
Interest Only Through Date	[1],[3]
Maturity Date	[1],[5]	Jun. 01, 2024
Outlook at Greystone [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 22,105	0
Interest Rate		4.30%
Interest Only Through Date		June 2021
Maturity Date		Jun. 01, 2025
Park & Kingston [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[6]	$ 18,432	18,432
Interest Rate	[6]	3.41%
Interest Only Through Date	[6]	Interest-only
Maturity Date	[6]	Apr. 01, 2020
Plantation Park [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 26,625	0
Interest Rate		4.64%
Interest Only Through Date		July 2024
Maturity Date		Jul. 01, 2028
Preston View [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 41,657	41,066
Interest Rate	[1]	3.85%
Interest Only Through Date	[1]	August 2022
Maturity Date	[1]	Aug. 01, 2025
Roswell City Walk [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 51,000	51,000
Interest Rate		3.63%
Interest Only Through Date		December 2019
Maturity Date		Dec. 01, 2026
Sorrel [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 38,684	38,684
Interest Rate	[1]	4.64%
Interest Only Through Date		November 2019
Maturity Date	[1]	May 01, 2023
Sovereign [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 28,227	28,788
Interest Rate		3.46%
Interest Only Through Date	[3]
Maturity Date		Nov. 10, 2022
The Brodie [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 34,825	34,825
Interest Rate		3.71%
Interest Only Through Date	[3]
Maturity Date		Dec. 01, 2023
The Links at Plum Creek [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 40,000	0
Interest Rate		4.31%
Interest Only Through Date		April 2020
Maturity Date		Oct. 01, 2025
The Mills [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 26,298	26,777
Interest Rate		4.21%
Interest Only Through Date	[3]
Maturity Date		Jan. 01, 2025
The Preserve at Henderson Beach [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 35,602	36,311
Interest Rate		4.65%
Interest Only Through Date	[3]
Maturity Date		Jan. 05, 2023
Veranda at Centerfield [Member] | Mortgages [Member] | Floating Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal	[1]	$ 26,100	0
Interest Rate	[1]	3.60%
Interest Only Through Date	[1]	July 2021
Maturity Date	[1],[7]	Jul. 26, 2023
Villages of Cypress Creek [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 26,200	26,200
Interest Rate		3.23%
Interest Only Through Date		October 2020
Maturity Date	[7]	Oct. 01, 2022
Wesley Village [Member] | Mortgages [Member] | Fixed Interest Rate [Member]
Line of Credit Facility [Line Items]
Total Outstanding Principal		$ 40,545	$ 40,545
Interest Rate		4.25%
Interest Only Through Date		April 2019
Maturity Date		Apr. 01, 2024

[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.

[2] ARIUM Grandewood has a fixed rate loan and a floating rate loan.

[3] The loan requires monthly payments of principal and interest.

[4] The principal balance includes a $16.2 million loan at a fixed rate of 3.97% and a $7.6 million supplemental loan at a fixed rate of 5.01%.

[5] The loan can be extended, subject to certain conditions, in connection with an election to convert to a fixed interest rate loan.

[6] The principal balance includes a $15.3 million loan at a fixed rate of 3.21% and a $3.2 million supplemental loan at a fixed rate of 4.34%.

[7] The loan has two one-year extension options subject to certain conditions.