Reportable Segments (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011 Store Customers Apartment State Property MilitaryHouse	Sep. 30, 2010 Store Customers	Sep. 30, 2011 Year Project Apartment Property Store Customers OptionPlan State MilitaryHouse	Sep. 30, 2010 Customers Store	Dec. 31, 2010
Rental income:
Rental income	$ 509,030,000	$ 451,832,000	$ 1,470,398,000	$ 1,311,377,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	184,959,000	179,478,000	545,213,000	523,993,000
NOI:
Net Operating Income	324,071,000	272,354,000	925,185,000	787,384,000
Total assets	15,756,817,000		15,756,817,000		16,184,194,000
Rental income	509,030,000	451,832,000	1,470,398,000	1,311,377,000
Reconciliation of NOI
Rental income	509,030,000	451,832,000	1,470,398,000	1,311,377,000
Property and maintenance expense	106,635,000	104,259,000	314,768,000	303,916,000
Real estate taxes and insurance expense	59,083,000	56,205,000	168,056,000	160,307,000
Property management expense	19,241,000	19,014,000	62,389,000	59,770,000
Operating expenses	(184,959,000)	(179,478,000)	(545,213,000)	(523,993,000)
Net Operating Income	324,071,000	272,354,000	925,185,000	787,384,000
Reportable Segments (Textuals) [Abstract]
Units in same store properties	104,922	104,922	102,129	102,129
Overhead Costs	100,000	100,000	300,000	400,000
Threshold limit of major customers	10.00%	10.00%	10.00%	10.00%
Number of customers accounted for threshold limit of major customers	0	0	0	0
Northeast [Member]
Rental income:
Rental income	191,776,000	168,082,000	553,452,000	482,090,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	68,899,000	68,505,000	204,531,000	192,592,000
NOI:
Net Operating Income	122,877,000	99,577,000	348,921,000	289,498,000
Total assets	6,313,643,000		6,313,643,000
Rental income	191,776,000	168,082,000	553,452,000	482,090,000
Reconciliation of NOI
Rental income	191,776,000	168,082,000	553,452,000	482,090,000
Operating expenses	(68,899,000)	(68,505,000)	(204,531,000)	(192,592,000)
Net Operating Income	122,877,000	99,577,000	348,921,000	289,498,000
Northeast [Member] | Same Store [Member]
Rental income:
Rental income	163,887,000	155,119,000	440,444,000	417,347,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	59,736,000	58,184,000	160,900,000	158,351,000
NOI:
Net Operating Income	104,151,000	96,935,000	279,544,000	258,996,000
Rental income	163,887,000	155,119,000	440,444,000	417,347,000
Reconciliation of NOI
Rental income	163,887,000	155,119,000	440,444,000	417,347,000
Operating expenses	(59,736,000)	(58,184,000)	(160,900,000)	(158,351,000)
Net Operating Income	104,151,000	96,935,000	279,544,000	258,996,000
Northeast [Member] | Non Same Store [Member]
Rental income:
Rental income	27,889,000	12,963,000	113,008,000	64,743,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	9,163,000	10,321,000	43,631,000	34,241,000
NOI:
Net Operating Income	18,726,000	2,642,000	69,377,000	30,502,000
Rental income	27,889,000	12,963,000	113,008,000	64,743,000
Reconciliation of NOI
Rental income	27,889,000	12,963,000	113,008,000	64,743,000
Operating expenses	(9,163,000)	(10,321,000)	(43,631,000)	(34,241,000)
Net Operating Income	18,726,000	2,642,000	69,377,000	30,502,000
Northwest [Member]
Rental income:
Rental income	98,320,000	87,127,000	284,530,000	251,465,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	35,100,000	33,660,000	101,964,000	95,576,000
NOI:
Net Operating Income	63,220,000	53,467,000	182,566,000	155,889,000
Total assets	2,656,529,000		2,656,529,000
Rental income	98,320,000	87,127,000	284,530,000	251,465,000
Reconciliation of NOI
Rental income	98,320,000	87,127,000	284,530,000	251,465,000
Operating expenses	(35,100,000)	(33,660,000)	(101,964,000)	(95,576,000)
Net Operating Income	63,220,000	53,467,000	182,566,000	155,889,000
Northwest [Member] | Same Store [Member]
Rental income:
Rental income	91,663,000	84,969,000	255,986,000	240,767,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	32,455,000	32,805,000	91,053,000	91,045,000
NOI:
Net Operating Income	59,208,000	52,164,000	164,933,000	149,722,000
Rental income	91,663,000	84,969,000	255,986,000	240,767,000
Reconciliation of NOI
Rental income	91,663,000	84,969,000	255,986,000	240,767,000
Operating expenses	(32,455,000)	(32,805,000)	(91,053,000)	(91,045,000)
Net Operating Income	59,208,000	52,164,000	164,933,000	149,722,000
Northwest [Member] | Non Same Store [Member]
Rental income:
Rental income	6,657,000	2,158,000	28,544,000	10,698,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	2,645,000	855,000	10,911,000	4,531,000
NOI:
Net Operating Income	4,012,000	1,303,000	17,633,000	6,167,000
Rental income	6,657,000	2,158,000	28,544,000	10,698,000
Reconciliation of NOI
Rental income	6,657,000	2,158,000	28,544,000	10,698,000
Operating expenses	(2,645,000)	(855,000)	(10,911,000)	(4,531,000)
Net Operating Income	4,012,000	1,303,000	17,633,000	6,167,000
Southeast [Member]
Rental income:
Rental income	94,752,000	88,965,000	278,221,000	262,736,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	37,111,000	36,784,000	110,385,000	108,973,000
NOI:
Net Operating Income	57,641,000	52,181,000	167,836,000	153,763,000
Total assets	2,514,066,000		2,514,066,000
Rental income	94,752,000	88,965,000	278,221,000	262,736,000
Reconciliation of NOI
Rental income	94,752,000	88,965,000	278,221,000	262,736,000
Operating expenses	(37,111,000)	(36,784,000)	(110,385,000)	(108,973,000)
Net Operating Income	57,641,000	52,181,000	167,836,000	153,763,000
Southeast [Member] | Same Store [Member]
Rental income:
Rental income	90,979,000	86,963,000	266,938,000	256,307,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	35,861,000	36,219,000	106,223,000	106,245,000
NOI:
Net Operating Income	55,118,000	50,744,000	160,715,000	150,062,000
Rental income	90,979,000	86,963,000	266,938,000	256,307,000
Reconciliation of NOI
Rental income	90,979,000	86,963,000	266,938,000	256,307,000
Operating expenses	(35,861,000)	(36,219,000)	(106,223,000)	(106,245,000)
Net Operating Income	55,118,000	50,744,000	160,715,000	150,062,000
Southeast [Member] | Non Same Store [Member]
Rental income:
Rental income	3,773,000	2,002,000	11,283,000	6,429,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	1,250,000	565,000	4,162,000	2,728,000
NOI:
Net Operating Income	2,523,000	1,437,000	7,121,000	3,701,000
Rental income	3,773,000	2,002,000	11,283,000	6,429,000
Reconciliation of NOI
Rental income	3,773,000	2,002,000	11,283,000	6,429,000
Operating expenses	(1,250,000)	(565,000)	(4,162,000)	(2,728,000)
Net Operating Income	2,523,000	1,437,000	7,121,000	3,701,000
Southwest [Member]
Rental income:
Rental income	121,641,000	108,994,000	350,909,000	318,579,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	42,511,000	40,287,000	122,025,000	117,000,000
NOI:
Net Operating Income	79,130,000	68,707,000	228,884,000	201,579,000
Total assets	3,230,549,000		3,230,549,000
Rental income	121,641,000	108,994,000	350,909,000	318,579,000
Reconciliation of NOI
Rental income	121,641,000	108,994,000	350,909,000	318,579,000
Operating expenses	(42,511,000)	(40,287,000)	(122,025,000)	(117,000,000)
Net Operating Income	79,130,000	68,707,000	228,884,000	201,579,000
Southwest [Member] | Same Store [Member]
Rental income:
Rental income	110,779,000	106,457,000	320,840,000	310,950,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	38,160,000	39,173,000	109,768,000	113,510,000
NOI:
Net Operating Income	72,619,000	67,284,000	211,072,000	197,440,000
Rental income	110,779,000	106,457,000	320,840,000	310,950,000
Reconciliation of NOI
Rental income	110,779,000	106,457,000	320,840,000	310,950,000
Operating expenses	(38,160,000)	(39,173,000)	(109,768,000)	(113,510,000)
Net Operating Income	72,619,000	67,284,000	211,072,000	197,440,000
Southwest [Member] | Non Same Store [Member]
Rental income:
Rental income	10,862,000	2,537,000	30,069,000	7,629,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	4,351,000	1,114,000	12,257,000	3,490,000
NOI:
Net Operating Income	6,511,000	1,423,000	17,812,000	4,139,000
Rental income	10,862,000	2,537,000	30,069,000	7,629,000
Reconciliation of NOI
Rental income	10,862,000	2,537,000	30,069,000	7,629,000
Operating expenses	(4,351,000)	(1,114,000)	(12,257,000)	(3,490,000)
Net Operating Income	6,511,000	1,423,000	17,812,000	4,139,000
Others [Member]
Rental income:
Rental income	2,541,000	(1,336,000)	3,286,000	(3,493,000)
Segment Reporting Information Operating Expenses Abstract
Operating expenses	1,338,000	242,000	6,308,000	9,852,000
NOI:
Net Operating Income	1,203,000	(1,578,000)	(3,022,000)	(13,345,000)
Total assets	1,042,030,000		1,042,030,000
Rental income	2,541,000	(1,336,000)	3,286,000	(3,493,000)
Reconciliation of NOI
Rental income	2,541,000	(1,336,000)	3,286,000	(3,493,000)
Operating expenses	(1,338,000)	(242,000)	(6,308,000)	(9,852,000)
Net Operating Income	1,203,000	(1,578,000)	(3,022,000)	(13,345,000)
Others [Member] | Non Same Store [Member]
Rental income:
Rental income	2,541,000	(1,336,000)	3,286,000	(3,493,000)
Segment Reporting Information Operating Expenses Abstract
Operating expenses	1,338,000	242,000	6,308,000	9,852,000
NOI:
Net Operating Income	1,203,000	(1,578,000)	(3,022,000)	(13,345,000)
Rental income	2,541,000	(1,336,000)	3,286,000	(3,493,000)
Reconciliation of NOI
Rental income	2,541,000	(1,336,000)	3,286,000	(3,493,000)
Operating expenses	(1,338,000)	(242,000)	(6,308,000)	(9,852,000)
Net Operating Income	1,203,000	(1,578,000)	(3,022,000)	(13,345,000)
Same Store [Member]
Rental income:
Rental income	457,308,000	433,508,000	1,284,208,000	1,225,371,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	166,212,000	166,381,000	467,944,000	469,151,000
NOI:
Net Operating Income	291,096,000	267,127,000	816,264,000	756,220,000
Rental income	457,308,000	433,508,000	1,284,208,000	1,225,371,000
Reconciliation of NOI
Rental income	457,308,000	433,508,000	1,284,208,000	1,225,371,000
Operating expenses	(166,212,000)	(166,381,000)	(467,944,000)	(469,151,000)
Net Operating Income	291,096,000	267,127,000	816,264,000	756,220,000
Non Same Store [Member]
Rental income:
Rental income	51,722,000	18,324,000	186,190,000	86,006,000
Segment Reporting Information Operating Expenses Abstract
Operating expenses	18,747,000	13,097,000	77,269,000	54,842,000
NOI:
Net Operating Income	32,975,000	5,227,000	108,921,000	31,164,000
Rental income	51,722,000	18,324,000	186,190,000	86,006,000
Reconciliation of NOI
Rental income	51,722,000	18,324,000	186,190,000	86,006,000
Operating expenses	(18,747,000)	(13,097,000)	(77,269,000)	(54,842,000)
Net Operating Income	$ 32,975,000	$ 5,227,000	$ 108,921,000	$ 31,164,000