Real Estate Activity (Consolidated Joint Venture) - Additional Information (Detail) $ in Thousands	Sep. 30, 2015 USD ($) Agreement	Aug. 31, 2015 Apartment	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)
Real Estate Properties [Line Items]
Number of units in real estate property | Agreement	23,723
Construction in progress	$ 108,531		$ 86,971
Cash and cash equivalents	62,959		140,512	$ 160,520	$ 82,110
Accounts payable, accrued expenses and other	79,241		$ 70,616
Consolidated Joint Venture [Member] | Denver, Colorado [Member]
Real Estate Properties [Line Items]
Number of units in real estate property | Apartment		358
Equity interest ownership percentage		92.50%
Construction in progress	18,710
Cash and cash equivalents	163
Accounts payable, accrued expenses and other	909
Noncontrolling equity interest	$ 1,371