Variable Interest Entities (Details) $ in Thousands	Mar. 31, 2016 USD ($) community Entity Apartment_home	Dec. 31, 2015 USD ($) community Entity Apartment_home	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Real Estate Investment Property, Net	$ 5,527,521	$ 5,529,461
Cash and Cash Equivalents, at Carrying Value	64,454	50,789	$ 164,490	$ 28,971
Assets	90,158	86,956
Secured Debt	3,811,510	3,822,141
Accrued liabilities and other	305,604	317,481
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Real Estate Investment Property, Net	1,190,106	1,201,998
Cash and Cash Equivalents, at Carrying Value	34,233	28,118
Assets	42,451	44,813
Secured Debt	955,424	959,523
Accrued liabilities and other	$ 27,756	$ 28,846
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 | community	16	17
Number of apartment homes owned by VIEs | Apartment_home	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	62	62,000
Number of Apartment Communities | community	48	48,000
Number of apartment homes owned by VIEs | Apartment_home	7,556	7,556,000