Investments in Real Estate (Details)	6 Months Ended
	Jun. 30, 2018 NumberofUnits
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Number of Units	2,800
Whetstone [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Durham, NC
Number of Units	204
Actual Or Estimated Initial Occupancy	3Q 2014
Actual Or Estimated Construction Completion	3Q 2015
Alexan CityCentre [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Houston, TX
Number of Units	340
Actual Or Estimated Initial Occupancy	2Q 2017
Actual Or Estimated Construction Completion	4Q 2017
Helios [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Atlanta, GA
Number of Units	282
Actual Or Estimated Initial Occupancy	2Q 2017
Actual Or Estimated Construction Completion	4Q 2017
Alexan Southside Place [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Houston, TX
Number of Units	270
Actual Or Estimated Initial Occupancy	4Q 2017
Actual Or Estimated Construction Completion	1Q 2018
Leigh House, formerly Lake Boone Trail [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Raleigh, NC
Number of Units	245
Actual Or Estimated Initial Occupancy	3Q 2017
Actual Or Estimated Construction Completion	4Q 2018
Vickers Historic Roswell, formerly Vickers Village [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Roswell, GA
Number of Units	79
Actual Or Estimated Initial Occupancy	2Q 2018
Actual Or Estimated Construction Completion	4Q 2018
Cade Boca Raton, formerly APOK Townhomes [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Boca Raton, FL
Number of Units	90
Actual Or Estimated Initial Occupancy	3Q 2018
Actual Or Estimated Construction Completion	1Q 2019
Arlo, formerly West Morehead [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Charlotte, NC
Number of Units	286
Actual Or Estimated Initial Occupancy	2Q 2018
Actual Or Estimated Construction Completion	2Q 2019
Domain at The One Forty, formerly Domain [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Garland, TX
Number of Units	299
Actual Or Estimated Initial Occupancy	2Q 2018
Actual Or Estimated Construction Completion	2Q 2019
Novel Perimeter, formerly Crescent Perimeter [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Atlanta, GA
Number of Units	320
Actual Or Estimated Initial Occupancy	4Q 2018
Actual Or Estimated Construction Completion	2Q 2019
Flagler Village [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Fort Lauderdale, FL
Number of Units	385
Actual Or Estimated Initial Occupancy	3Q 2019
Actual Or Estimated Construction Completion	3Q 2020
ARIUM at Palmer Ranch [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Sarasota, FL
Number of Units	320
Year Build/Renovated	2016	[1]
Ownership Interest	100.00%
ARIUM Grandewood [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	306
Year Build/Renovated	2005	[1]
Ownership Interest	100.00%
ARIUM Gulfshore [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Naples, FL
Number of Units	368
Year Build/Renovated	2016	[1]
Ownership Interest	100.00%
ARIUM Palms [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	252
Year Build/Renovated	2008	[1]
Ownership Interest	95.00%
ARIUM Pine Lakes [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Port St. Lucie, FL
Number of Units	320
Year Build/Renovated	2003	[1]
Ownership Interest	85.00%
ARIUM Westside [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Atlanta, GA
Number of Units	336
Year Build/Renovated	2008	[1]
Ownership Interest	90.00%
Ashton Reserve [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Charlotte, NC
Number of Units	473
Year Build/Renovated	2015	[1]
Ownership Interest	100.00%
Citrus Tower [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	336
Year Build/Renovated	2006	[1]
Ownership Interest	96.80%
Enders Place at Baldwin Park [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	220
Year Build/Renovated	2003	[1]
Ownership Interest	92.00%
James at South First [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Austin, TX
Number of Units	250
Year Build/Renovated	2016	[1]
Ownership Interest	90.00%
Marquis at Crown Ridge [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	San Antonio, TX
Number of Units	352
Year Build/Renovated	2009	[1]
Ownership Interest	90.00%
Marquis at Stone Oak [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	San Antonio, TX
Number of Units	335
Year Build/Renovated	2007	[1]
Ownership Interest	90.00%
Marquis at The Cascades [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Tyler, TX
Number of Units	582
Year Build/Renovated	2009	[1]
Ownership Interest	90.00%
Marquis at TPC [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	San Antonio, TX
Number of Units	139
Year Build/Renovated	2008	[1]
Ownership Interest	90.00%
Park & Kingston [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Charlotte, NC
Number of Units	168
Year Build/Renovated	2015	[1]
Ownership Interest	100.00%
Preston View [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Morrisville, NC
Number of Units	382
Year Build/Renovated	2000	[1]
Ownership Interest	100.00%
Roswell City Walk [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Roswell, GA
Number of Units	320
Year Build/Renovated	2015	[1]
Ownership Interest	98.00%
Sorrel [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Frisco, TX
Number of Units	352
Year Build/Renovated	2015	[1]
Ownership Interest	95.00%
Sovereign [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Fort Worth, TX
Number of Units	322
Year Build/Renovated	2015	[1]
Ownership Interest	95.00%
Average [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Number of Units	10,374
The Brodie [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Austin, TX
Number of Units	324
Year Build/Renovated	2001	[1]
Ownership Interest	92.50%
The Preserve at Henderson Beach [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Destin, FL
Number of Units	340
Year Build/Renovated	2009	[1]
Ownership Interest	100.00%
Villages at Cypress Creek [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Houston, TX
Number of Units	384
Year Build/Renovated	2001	[1]
Ownership Interest	80.00%
Wesley Village [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Charlotte, NC
Number of Units	301
Year Build/Renovated	2010	[1]
Ownership Interest	100.00%
ARIUM Glenridge [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Atlanta, GA
Number of Units	480
Year Build/Renovated	1990	[1]
Ownership Interest	90.00%
ARIUM Hunter's Creek [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	532
Year Build/Renovated	1999	[1]
Ownership Interest	100.00%
ARIUM Metrowest [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Orlando, FL
Number of Units	510
Year Build/Renovated	2001	[1]
Ownership Interest	100.00%
Outlook at Greystone [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Birmingham, AL
Number of Units	300
Year Build/Renovated	2007	[1]
Ownership Interest	100.00%
The Links at Plum Creek [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Castle Rock, CO
Number of Units	264
Year Build/Renovated	2000	[1]
Ownership Interest	88.00%
The Mills [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Greenville, SC
Number of Units	304
Year Build/Renovated	2013	[1]
Ownership Interest	100.00%
Plantation Park [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Lake Jackson, TX
Number of Units	238
Year Build/Renovated	2016	[1]
Ownership Interest	80.00%
Sands Parc [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real Estate Property Location	Daytona Beach, FL
Number of Units	264
Year Build/Renovated	2017	[1]
Ownership Interest	100.00%

[1] Represents date of last significant renovation or year built if there were no renovations.