Significant Transactions, Dispositions of Apartment Communities and Assets Held for Sale (Details Textual)	3 Months Ended
	Mar. 31, 2019 USD ($) apartment_home Property	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Noncontrolling Interest in Limited Partnerships	$ (2,857,000)		$ (2,967,000)
Gain (loss) on dispositions of real estate and the Asset Management business, inclusive of related income tax	291,473,000	$ 53,195,000
Assets	6,283,769,000		6,190,004,000
Liabilities	4,222,302,000		$ 4,325,072,000
Gain (Loss) on Sale of Properties, before Applicable Income Taxes	$ 291,473,000	$ 53,195,000
Wholly And Partially Owned Consolidated Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of apartment homes in apartment communities | apartment_home	34,207
Number of apartment communities | Property	124
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Wholly And Partially Owned Consolidated Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of apartment homes in apartment communities | apartment_home	2,206
Number of apartment communities | Property	7
Gain (Loss) on Sale of Properties, before Applicable Income Taxes	$ 291,473