Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of reportable operating segments (in segments) | segment			3
Net operating income	$ 256,069	$ 262,331	$ 796,689	$ 782,364
Corporate-level property management expenses	(8,619)	(8,553)	(26,024)	(25,451)
Depreciation and amortization	(130,202)	(120,809)	(395,370)	(360,842)
General and administrative	(13,310)	(11,345)	(42,244)	(38,731)
Expensed acquisition and investment related costs	(2)	(13)	(104)	(69)
Gain on sale of real estate and land	22,654	0	39,251	0
Interest expense	(55,430)	(54,896)	(165,024)	(162,651)
Total return swap income	2,977	2,154	7,749	6,174
Interest and other income	6,512	8,685	12,696	29,293
Equity income from co-investments	14,960	21,700	53,514	54,935
Deferred tax expense on unrealized gain on unconsolidated co-investment	0	(1,457)	(1,636)	(1,457)
(Loss) gain on early retirement of debt, net	(19,114)	5,475	(23,820)	7,143
Gain on remeasurement of co-investment	0	0	234,694	31,535
Net income	78,842	105,700	497,683	329,266
Net reportable operating segment - real estate assets	11,085,982		11,085,982		$ 10,348,660
Real estate under development	364,875		364,875		546,075
Co-investments	1,018,235		1,018,235		1,335,339
Real estate held for sale, net	32,878		32,878		0
Cash and cash equivalents, including restricted cash	569,075	91,726	569,075	91,726	81,094	$ 151,395
Marketable securities	134,971		134,971		144,193
Notes and other receivables	75,432		75,432		134,365
Operating lease right-of-use assets	72,910		72,910		74,744
Prepaid expenses and other assets	46,684		46,684		40,935
Total assets	13,401,042		13,401,042		12,705,405
Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	368,464	364,504	1,126,363	1,077,767
Management and Other Fees From Affiliates Income
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	2,347	2,428	7,312	7,023
Operating Segments | Southern California
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	94,163	106,926	303,328	322,891
Net reportable operating segment - real estate assets	4,089,875		4,089,875		4,199,377
Operating Segments | Southern California | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	140,271	151,841	438,087	453,873
Operating Segments | Northern California
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	103,657	103,232	332,566	304,975
Net reportable operating segment - real estate assets	5,566,802		5,566,802		4,408,404
Operating Segments | Northern California | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	148,712	140,509	462,558	411,694
Operating Segments | Seattle Metro
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	41,216	43,401	126,422	128,081
Net reportable operating segment - real estate assets	1,417,753		1,417,753		1,456,187
Operating Segments | Seattle Metro | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	60,617	61,052	184,310	180,942
Other real estate assets
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	17,033	8,772	34,373	26,417
Net reportable operating segment - real estate assets	11,552		11,552		$ 284,692
Other real estate assets | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 18,864	$ 11,102	$ 41,408	$ 31,258