Organization, Basis of Presentation and Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) state community home $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) state community home $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares
Organization and Basis of Presentation
Number of operating apartment communities | community	257		257
Number of apartment homes included in operating apartment communities owned | home	74,857		74,857
Number of states where operating apartment communities owned are located | state	11		11
Number of communities with apartments under reconstruction | community	7		7
Number of apartment homes under reconstruction | home	2,787		2,787
Number of owned communities under construction | community	26		26
Expected number of apartment homes under construction | home	8,117		8,117
Communities under development rights | community	34		34
Estimated number of apartment homes in communities to be developed | home	10,080		10,080
Weighted Average Number of Shares Outstanding, Basic | shares	131,977,578	129,856,335	131,930,916	129,574,118
Weighted Average Number of Limited Partnership and General Partnership Unit Outstanding, Basic and Diluted | shares	7,500	7,500	7,500	7,500
Weighted Average Number Diluted Shares Outstanding Adjustment | shares	1,101,361	384,486	1,192,947	356,614
Earnings Per Share, Basic | $ / shares	$ 1.30	$ 1.22	$ 2.88	$ 2.31
Weighted Average Number of Shares Outstanding, Diluted | shares	133,086,439	130,248,321	133,131,363	129,938,232
Net Income (Loss) Available to Common Stockholders, Basic	$ 172,324	$ 158,086	$ 380,469	$ 299,825
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	445	254	975	487
Undistributed Earnings, Basic	171,879	157,832	379,494	299,338
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	(9)	(9)	(19)	(17)
Net Income (Loss) Available to Common Stockholders, Diluted	$ 172,333	$ 158,095	$ 380,488	$ 299,842
Earnings Per Share, Diluted | $ / shares	$ 1.29	$ 1.21	$ 2.86	$ 2.31