Significant Transactions During the Six Months Ended June 30, 2019 and Subsequent Events (Details)	1 Months Ended						3 Months Ended		6 Months Ended
	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	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
Other Commitments [Line Items]
Repayments of secured debt				$ 86,000,000.0		$ 290,000,000.0
Gain on remeasurement of co-investment				31,500,000			$ 0	$ 0	$ 31,535,000	$ 0
Promote income				800,000
Debt assumed in connection with acquisition									98,681,000	0
Gain on sale of real estate and land							0	22,244,000	0	22,244,000
Proceeds from full redemption of a preferred equity investment in a joint venture					$ 10,900,000
Early redemption fee					100,000
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
Debt, stated interest rate						5.57%
Gain on early retirement of debt, net						$ 1,400,000	332,000	$ 0	1,668,000	$ 0
Senior Notes [Member] | Unsecured Notes, 4.0% Interest Rate, Due March 2029 [Member]
Other Commitments [Line Items]
Debt, face amount	$ 150,000,000.0				$ 350,000,000.0		$ 150,000,000.0		$ 150,000,000.0
Debt, stated interest rate					4.00%
Debt offering price, percentage of par value	100.717%				99.188%		100.717%		100.717%
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
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%
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	12,000,000.0						$ 12,000,000.0		$ 12,000,000.0
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	5,000,000.0						5,000,000.0		5,000,000.0
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	$ 4,000,000.0						$ 4,000,000.0		$ 4,000,000.0
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
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