Variable Interest Entities (Details) $ in Thousands	Sep. 30, 2016 USD ($) Entity Units Property	Dec. 31, 2015 USD ($) Entity Units Property	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Real Estate Investment Property, Net	$ 5,755,678	$ 5,529,461
Cash and Cash Equivalents, at Carrying Value	47,908	50,789	$ 45,241	$ 28,971
Restricted cash	109,511	86,956
Assets held for sale	50,968	3,070
Other Assets	329,782	448,405
Secured Debt	3,760,761	3,822,141
Accrued liabilities and other	212,046	317,481
Liabilities related to assets held for sale	1,018	53
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Real Estate Investment Property, Net	1,147,334	1,201,998
Cash and Cash Equivalents, at Carrying Value	26,495	28,118
Restricted cash	42,534	44,813
Assets held for sale	21,685	0
Secured Debt	967,993	959,523
Accrued liabilities and other	34,794	28,846
Liabilities related to assets held for sale	$ 448	$ 0
Conventional Apartment Communities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Number of consolidated variable interest entities | Entity	12	13
Number of Apartment Communities | Property	16	17
Number of apartment homes owned by VIEs | Units	5,993	6,089
Affordable Apartment Communities [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Number of consolidated variable interest entities | Entity	60	62
Number of Apartment Communities | Property	47	48
Number of apartment homes owned by VIEs | Units	7,260	7,556