Significant Transactions During the Nine Months Ended September 30, 2019 and Subsequent Events (Details)	1 Months Ended									3 Months Ended		9 Months Ended
	Oct. 25, 2019 USD ($)	Sep. 30, 2019 USD ($) apartment $ / shares	Aug. 31, 2019 USD ($) apartment	Jun. 30, 2019 USD ($) apartment	May 31, 2019 USD ($)	Apr. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Feb. 28, 2019 USD ($)	Jan. 31, 2019 USD ($) shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)	Aug. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Other Commitments [Line Items]
Repayments of secured debt		$ 289,100,000							$ 290,000,000.0
Gain on remeasurement of co-investment										$ 0	$ 0	$ 31,535,000	$ 0
Debt assumed in connection with acquisition												143,006,000	0
Gain on sale of real estate and land										0	0	0	22,244,000
Ownership interest of initial equity commitment		1,413,861,000								1,413,861,000		1,413,861,000			$ 1,300,140,000
Shares repurchased during period (in shares) | shares									234,061
Shares repurchased during period, value									$ 57,000,000.0
Purchase authority remaining under stock repurchase plan		$ 250,000,000.0						$ 250,000,000.0		250,000,000.0		250,000,000.0
Sale of common stock, net										$ 72,631,000	(130,000)	$ 72,549,000	(483,000)
Senior unsecured debt of coupon rate		5.69%							5.57%	5.69%		5.69%
Proceeds from issuance of debt												$ 892,762,000	298,773,000
Gain on early retirement of debt, net		$ 5,500,000							$ 1,400,000	$ 5,475,000	$ 0	$ 7,143,000	$ 0
Subsequent Event [Member]
Other Commitments [Line Items]
Proceeds from full redemption of a preferred equity investment in a joint venture	$ 15,800,000
Early redemption fee	200,000
Senior Notes [Member] | Unsecured Notes, 4.0% Interest Rate, Due March 2029 [Member]
Other Commitments [Line Items]
Operating partner issued senior unsecured debt notes							$ 150,000,000.0	$ 350,000,000.0
Senior unsecured debt of coupon rate								4.00%
Debt offering price, percentage of par value							100.717%	99.188%
Senior Notes [Member] | Unsecured Notes, 3.0% Interest Rate, Due January 2030 [Member]
Other Commitments [Line Items]
Operating partner issued senior unsecured debt notes			$ 400,000,000.0
Senior unsecured debt of coupon rate			3.00%
Debt offering price, percentage of par value			98.632%
Senior Notes [Member] | Unsecured Notes, 3.000% Interest Rate, Due January 2020 [Member] | Subsequent Event [Member]
Other Commitments [Line Items]
Proceeds from issuance of debt	$ 150,000,000.0
Debt offering price, percentage of par value	101.685%
Common Stock [Member]
Other Commitments [Line Items]
Sale of common stock, net (in shares) | shares										228,000		228,271
Common stock dividends (in dollars per share) | $ / shares		$ 321.56								$ 321.56		$ 321.56
Sale of common stock, net												$ 73,400,000
Brio, Walnut Creek, California [Member]
Other Commitments [Line Items]
Number of units acquired | apartment				300
Payments to acquire real estate				$ 164,900,000
Debt assumed in connection with acquisition				$ 98,700,000
Wesco V, LLC (Wesco V), Emeryville [Member]
Other Commitments [Line Items]
Number of units acquired | apartment			331
Payments to acquire real estate			$ 178,000,000.0
Debt assumed in connection with acquisition			$ 89,000,000.0
Wesco V, LLC (Wesco V), Emeryville [Member] | Loan of (LIBOR) [Member]
Other Commitments [Line Items]
Loan of the Company with an interest rate of LIBOR														1.30%
BEX IV, LLC (BEX IV), Menlo Park [Member]
Other Commitments [Line Items]
Number of units acquired | apartment			195
Payments to acquire real estate			$ 148,000,000.0
Debt assumed in connection with acquisition			$ 44,400,000
BEX IV, LLC (BEX IV), Menlo Park [Member] | Loan of (LIBOR) [Member]
Other Commitments [Line Items]
Loan of the Company with an interest rate of LIBOR														3.25%
Redwood City [Member]
Other Commitments [Line Items]
Number of units acquired | apartment		132
Payments to acquire real estate		$ 88,700,000
Acquisition of company assumed mortgage debt		44,300,000								$ 44,300,000		44,300,000
BEX IV,Ownership Interest In The Joint Venture [Member]
Other Commitments [Line Items]
Limited partnership interest in partnership investments			50.10%
Ownership interest of initial equity commitment														$ 52,200,000
Multifamily Development in Mountain View, California [Member]
Other Commitments [Line Items]
Commitment to fund preferred equity investment								$ 24,500,000
Preferred returns rate								11.00%
San Jose, CA [Member]
Other Commitments [Line Items]
Proceeds from full redemption of a preferred equity investment in a joint venture								$ 10,900,000
Early redemption fee								$ 100,000
Multifamily Development Community in Irvine, California [Member]
Other Commitments [Line Items]
Commitment to fund preferred equity investment							$ 36,000,000.0
Preferred returns rate							10.15%
Funded commitment amount		21,600,000								21,600,000		21,600,000
Joint Venture that Holds Property in Santa Ana, California [Member]
Other Commitments [Line Items]
Proceeds from full redemption of a preferred equity investment in a joint venture						$ 16,300,000
Early redemption fee						700,000
Multifamily Development In Oakland, California, 10.25% Rate [Member]
Other Commitments [Line Items]
Commitment to fund preferred equity investment						$ 36,800,000
Preferred returns rate						10.25%
Funded commitment amount		15,000,000.0								15,000,000.0		15,000,000.0
Multifamily Development In Oakland, California, 11.0% Rate [Member]
Other Commitments [Line Items]
Commitment to fund preferred equity investment						$ 11,800,000
Preferred returns rate						11.00%
Funded commitment amount		5,500,000								5,500,000		5,500,000
Redmond, WA [Member]
Other Commitments [Line Items]
Proceeds from full redemption of a preferred equity investment in a joint venture		14,800,000
Early redemption fee		300,000								300,000		300,000
Seattle, WA [Member]
Other Commitments [Line Items]
Proceeds from full redemption of a preferred equity investment in a joint venture		16,300,000
Early redemption fee		$ 1,400,000								$ 1,400,000		$ 1,400,000
One South Market, San Jose, CA [Member]
Other Commitments [Line Items]
Limited partnership interest in partnership investments							45.00%
Payments to joint venture interest							$ 80,600,000
Repayments of secured debt							86,000,000.0
Gain on remeasurement of co-investment							31,500,000
Promote income							$ 800,000
Land Located in Oakland, California [Member]
Other Commitments [Line Items]
Limited partnership interest in partnership investments					50.00%
Proceeds from sale of real estate					$ 6,100,000
Gain on sale of real estate and land					$ 900,000