Investments in Unconsolidated Real Estate Entities - Summary of Financial Information for Apartment LLCs (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Real Estate Properties [Line Items]
Real estate assets, net of accumulated depreciation of $53,466 and $52,012 at September 30, 2015 and December 31, 2014, respectively	$ 2,181,641	$ 2,128,767
Total assets	2,288,894	2,311,798
Total liabilities	1,031,668	1,018,752
Members' equity	1,250,198	1,285,960	$ 1,290,444	$ 1,152,731
Total liabilities, redeemable common units and equity	2,288,894	2,311,798
Unconsolidated Properties [Member]
Real Estate Properties [Line Items]
Real estate assets, net of accumulated depreciation of $53,466 and $52,012 at September 30, 2015 and December 31, 2014, respectively	208,287	208,493
Cash and other	6,512	5,490
Total assets	214,799	213,983
Mortgage notes payable	177,723	177,723
Other liabilities	2,535	3,445
Total liabilities	180,258	181,168
Members' equity	34,541	32,815
Total liabilities, redeemable common units and equity	214,799	213,983
Unconsolidated Properties [Member] | Apartment LLC [Member]
Real Estate Properties [Line Items]
Company's equity investment in Apartment LLCs	$ (11,899)	$ (12,565)