Real Estate Investments - Development Co-Investments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) unit	Dec. 31, 2019 USD ($) unit	Dec. 31, 2018 USD ($) unit	Dec. 31, 2015 USD ($) unit
Real Estate Properties [Line Items]
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures		$ 1,335,339	$ 1,300,140
Number of units to be developed | unit		1,960
Total Operating Co-investments
Real Estate Properties [Line Items]
Number of apartments owned through joint ventures | unit		10,672	10,613
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures		$ 743,461	$ 833,270
Total Development Co-Investments
Real Estate Properties [Line Items]
Number of apartments owned through joint ventures | unit		806	814
Investments in (distributions in excess of investments in) and advance to affiliates, subsidiaries, associates and joint ventures		$ 146,944	$ 94,060
Ohlone Multi-Family Community
Real Estate Properties [Line Items]
Number of units to be developed | unit	269
Equity method investment, ownership percentage	50.00%
Estimated cost active development projects	$ 136,000
Commitment to fund preferred equity investment in the project	$ 28,900
Annualized preferred return rate	10.00%
Folsom 500
Real Estate Properties [Line Items]
Number of units to be developed | unit				537
Equity method investment, ownership percentage				50.00%
Estimated cost active development projects				$ 415,000