Investments in Unconsolidated Real Estate Entities - Summary of Financial Information for Apartment LLCs (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Real Estate Properties [Line Items]
Real estate assets, net of accumulated depreciation of $38,332 and $32,780 at December 31, 2012 and 2011, respectively	$ 2,191,708	$ 2,075,517
Total assets	2,363,364	2,139,064
Total liabilities	1,236,585	1,084,701
Members' equity	1,119,620	1,047,523	967,295	1,016,053
Total liabilities and members' equity	2,363,364	2,139,064
Apartment LLCs [Member]
Real Estate Properties [Line Items]
Real estate assets, net of accumulated depreciation of $38,332 and $32,780 at December 31, 2012 and 2011, respectively	212,877	217,443
Assets held for sale, net		28,846
Cash and other	5,103	6,526
Total assets	217,980	252,815
Mortgage notes payable	177,723	206,495
Other liabilities	2,588	2,737
Total liabilities	180,311	209,232
Members' equity	37,669	43,583
Total liabilities and members' equity	217,980	252,815
Company's equity investment in Apartment LLCs	$ (11,764)	$ (8,601)