Organization and Basis of Presentation (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012 state home community	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 property state home community	Dec. 31, 2011	Dec. 31, 2010
Organization and Basis of Presentation
Number of operating apartment communities owned	180								180
Number of apartment homes included in operating apartment communities owned	52,792								52,792
Number of states where operating apartment communities owned are located	9								9
Number of communities with apartments under reconstruction	5								5
Number of apartment homes under reconstruction	1,787								1,787
Number of owned communities under construction	23								23
Expected number of apartment homes under construction	6,599								6,599
Communities under development rights	34								34
Estimated number of apartment homes in communities to be developed	9,602								9,602
Period of lease									1 year
Number of land parcels acquired under development rights									4
Number of land parcels acquired under development rights for which the Company is actively pursuing development									3
Real Estate
Minimum percentage of distribution of adjusted taxable income for deducting dividends from federally taxable income									90.00%
Minimum percentage of distribution of REIT taxable income for federal income tax exemption									100.00%
Refunds of federal excise taxes									$ 235,000
Reconciliation of net income attributable to common stockholders to taxable net income
Net income attributable to common stockholders	122,356,000	86,844,000	156,909,000	57,758,000	323,085,000	44,824,000	43,373,000	30,341,000	423,869,000	441,622,000	175,331,000
GAAP gain on sale of communities (in excess of) less than tax gain									37,575,000	(84,152,000)	3,812,000
Depreciation/amortization timing differences on real estate									15,012,000	9,192,000	8,266,000
Tax compensation expense less than (in excess of) GAAP									(19,218,000)	(43,145,000)	(12,202,000)
Impairment loss									1,449,000	14,052,000
Other adjustments									(3,202,000)	183,000	12,628,000
Taxable net income									455,485,000	337,752,000	187,835,000
Tax components of common stock dividends declared
Ordinary income (as a percent)									47.00%	34.00%	74.00%
15% capital gain (as a percent)									33.00%	47.00%	11.00%
Unrecaptured Section 1250 gain (as a percent)									20.00%	19.00%	15.00%
Deferred Financing Costs
Accumulated amortization of deferred financing costs	20,773,000				17,574,000				20,773,000	17,574,000
Buildings and Building Improvements
Real Estate
Capitalization of minimum improvements and upgrades	15,000								15,000
Buildings and Building Improvements | Minimum
Real Estate
Estimated useful life of buildings and improvements									7 years
Buildings and Building Improvements | Maximum
Real Estate
Estimated useful life of buildings and improvements									30 years
Computers and furniture
Real Estate
Capitalization of minimum improvements and upgrades	$ 2,500								$ 2,500
Computers and furniture | Minimum
Real Estate
Estimated useful life of buildings and improvements									3 years
Computers and furniture | Maximum
Real Estate
Estimated useful life of buildings and improvements									7 years