Segment Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) segment	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Revenues from External Customers and Long-Lived Assets [Line Items]
Number of reportable segments | segment	3
Number of operating segments | segment	3
Net operating income	$ 242,397	$ 282,607
Corporate-level property management expenses	(8,947)	(8,759)
Depreciation and amortization	(128,587)	(131,559)
General and administrative	(9,812)	(13,982)
Expensed acquisition and investment related costs	(15)	(87)
Gain on sale of real estate and land	100,096	0
Interest expense	(51,649)	(55,147)
Total return swap income	2,844	1,984
Interest and other income (loss)	14,387	(5,221)
Equity income from co-investments	17,011	21,297
Deferred tax expense on unrealized gain on unconsolidated co-investment	(508)	0
(Loss) gain on early retirement of debt, net	(2,517)	321
Gain on remeasurement of co-investment	0	234,694
Net income	176,949	328,765
Net reportable operating segment - real estate assets	10,718,771		$ 10,927,786
Real estate under development	404,496		386,047
Co-investments	962,625		1,018,010
Real estate held for sale	0		57,938
Cash and cash equivalents, including restricted cash	113,360	282,347	84,041	$ 81,094
Marketable securities	165,265		147,768
Notes and other receivables	266,896		195,104
Operating lease right-of-use assets	71,347		72,143
Prepaid expenses and other assets	87,444		47,340
Total assets	12,790,204		12,936,177
Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	352,876	389,750
Management and Other Fees From Affiliates Income
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	2,249	2,617
Operating Segments | Southern California
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	99,251	108,289
Net reportable operating segment - real estate assets	3,956,663		3,993,275
Operating Segments | Southern California | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	143,012	151,895
Operating Segments | Northern California
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	101,625	117,187
Net reportable operating segment - real estate assets	5,363,795		5,408,019
Operating Segments | Northern California | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	146,690	158,456
Operating Segments | Seattle Metro
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	38,779	44,426
Net reportable operating segment - real estate assets	1,389,142		1,403,678
Operating Segments | Seattle Metro | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	58,633	63,044
Other real estate assets
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	2,742	12,705
Net reportable operating segment - real estate assets	9,171		$ 122,814
Other real estate assets | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 4,541	$ 16,355