Disposals and Discontinued Operations (Details Textual) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014 Units Property	Sep. 30, 2013 Units Property	Sep. 30, 2014 Units Property PartnershipUnit	Sep. 30, 2013 Property Units	Dec. 31, 2013 Units Property
Long Lived Assets Held-for-sale [Line Items]
Number of consolidated apartment communities disposed	15	8	26	13	29
Number of apartment homes in consolidated apartment communities disposed	4,635	2,280	8,368	2,510	6,953
Income (loss) from continuing operations	$ 18,186,000	$ 6,975,000	$ 48,169,000	$ 7,791,000
Gain on dispositions of real estate, net of tax	126,329,000	0	262,483,000	0
Income Taxes on Dispositions of Apartment Communities	21,100,000		29,800,000
Prepayment penalties treated as reduction of gain upon repayment of property loans collateralized by apartment communities sold	13,600,000	5,400,000	22,100,000	6,400,000
Number of unconsolidated partnership interests sold			10
Number of apartment homes in unconsolidated partnership interest sold			439
Gross proceeds from sale of unconsolidated partnership interests			100,000
Non-recourse property debt assumed in connection with real estate dispositions			56,900,000	48,300,000
Provision for real estate impairment losses	1,413,000	0	1,413,000	0
Assets Held-for-sale [Member]
Long Lived Assets Held-for-sale [Line Items]
Number of Apartment Communities	5		5
Number of Apartment Homes in Apartment Communities	667		667
Sold Apartment Communities [Member]
Long Lived Assets Held-for-sale [Line Items]
Income (loss) from continuing operations	$ 2,500,000		$ 16,000,000