Organization and Basis of Presentation - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2011	Dec. 31, 2011 Property Community Home Location	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of operating apartment communities owned		181
Number of apartment homes included in operating apartment communities owned		53,294
Number of states where operating apartment communities owned are located		10
Number of communities with apartments under reconstruction		13
Number of apartment homes under reconstruction		3,338
Number of owned communities under construction		19
Expected number of apartment homes under construction		5,244
Communities under development rights		32
Expected number of apartment homes in communities to be developed		9,012
Number of parcels of land acquired under development rights		14
Number of parcels of land acquired under development rights for which the Company intend to pursue development		4
Number of parcels of land acquired under development rights for which the Company does not intend to pursue development		4
Net charges (refunds) for federal excise taxes			$ (235,000)	$ 515,000
Minimum percentage of taxable income distribution to maintain REIT status		90.00%
Percentage distribution of taxable income required to not be subject to federal income tax		100.00%
Accumulated amortization of deferred financing costs		17,574,000	23,215,000
Options to purchase shares of common stock excluded from computation of earnings per share amount		457,419	326,366
Costs related to abandoned pursuits, abandonment of development rights and disposition pursuits		1,957,000	2,741,000	5,842,000
Number of impaired parcels of land		2
Impairment loss - land holdings	14,052,000	14,052,000		21,152,000	9,952,000
Impairment of investment in unconsolidated joint venture		1,955,000
Equity in income of unconsolidated entities, impairment loss				2,600,000
Cash Flow Hedges | Variable rate notes
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Notional amount debt, interest rate derivatives		640,006,000	210,421,000
Fair Value Hedge | Fixed rate notes
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Notional amount debt, interest rate derivatives		75,000,000	225,000,000
Interest Rate Caps | Variable rate notes
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Notional amount debt, interest rate derivatives		79,835,000	109,020,000
Minimum
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Improvements and upgrades amount to be capitalized		15,000
Computers and furniture amount to be capitalized		$ 2,500
Buildings and Building Improvements
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Estimated useful lives, minimum		7
Estimated useful lives, maximum		30
Furniture, Fixtures and Equipment
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Estimated useful lives, minimum		3
Estimated useful lives, maximum		7