Investments in Unconsolidated Real Estate Entities - Schedule of Operation for Apartment LLCs (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues
Rental									$ 315,176	$ 286,518	$ 268,090
Other property revenues									18,885	17,880	16,053
Total revenues	86,101	86,374	82,160	80,276	77,749	78,612	75,424	73,531	334,911	305,316	285,138
Expenses
Property operating and maintenance									143,678	132,410	131,378
Interest									46,419	56,791	54,613
Total expenses									242,883	226,369	262,241
Net income (loss)									83,939	25,466	(6,960)
Company's share of net income in Apartment LLCs									7,995	1,001	18,739
Apartment LLCs [Member]
Revenues
Rental									24,659	23,504	22,444
Other property revenues									1,844	1,823	1,718
Total revenues									26,503	25,327	24,162
Expenses
Property operating and maintenance									10,541	9,896	9,945
Depreciation and amortization									5,768	5,934	5,836
Interest									9,181	10,247	10,247
Total expenses									25,490	26,077	26,028
Net loss from continuing operations									1,013	(750)	(1,866)
Gain (loss) from discontinued operations									21,667	(151)	(254)
Net income (loss)									22,680	(901)	(2,120)
Company's share of net income in Apartment LLCs									$ 7,995	$ 1,001	$ 635