Summary of Properties Classified as Held for Sale (Detail)	9 Months Ended
	Sep. 30, 2018 USD ($) Property	Dec. 31, 2017 USD ($)
Real Estate Properties [Line Items]
Number of units located with multifamily properties | Property	15,860
Net Carrying Value | $	$ 141,853,000	$ 0
Held-for-sale
Real Estate Properties [Line Items]
Number of units located with multifamily properties | Property	1,348
Net Carrying Value | $	$ 141,853,000	$ 0
Held-for-sale | Reserve At Eagle Ridge [Member]
Real Estate Properties [Line Items]
Location	Waukegan, IL
Number of units located with multifamily properties | Property	370
Net Carrying Value | $	$ 26,941,000
Held-for-sale | Carrington Park [Member]
Real Estate Properties [Line Items]
Location	Little Rock, AR
Number of units located with multifamily properties | Property	202
Net Carrying Value | $	$ 20,581,000
Held-for-sale | Arbors At The Reservoir [Member]
Real Estate Properties [Line Items]
Location	Ridgeland, MS
Number of units located with multifamily properties | Property	170
Net Carrying Value | $	$ 19,411,000
Held-for-sale | Stonebridge At The Ranch [Member]
Real Estate Properties [Line Items]
Location	Little Rock, AR
Number of units located with multifamily properties | Property	260
Net Carrying Value | $	$ 29,598,000
Held-for-sale | Aventine Greenville [Member]
Real Estate Properties [Line Items]
Location	Greenville, SC
Number of units located with multifamily properties | Property	346
Net Carrying Value | $	$ 45,322,000