Segment Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of reportable operating segments defined by geographical regions | segment	3
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	$ 1,486,150	$ 1,450,628	$ 1,390,870
Total net operating income	1,045,750	1,054,101	1,006,529
Management and other fees from affiliates	9,598	9,527	9,183
Corporate-level property management expenses	(34,573)	(34,067)	(32,055)
Depreciation and amortization	(525,497)	(483,750)	(479,884)
General and administrative	(65,388)	(54,262)	(53,451)
Expensed acquisition and investment related costs	(1,591)	(168)	(194)
Impairment loss	(1,825)	(7,105)	0
Gain (loss) on sale of real estate and land	64,967	(3,164)	61,861
Interest expense	(220,633)	(217,339)	(220,492)
Total return swap income	10,733	8,446	8,707
Interest and other income	40,999	46,298	23,010
Equity income from co-investments	66,512	112,136	89,132
Deferred tax expense on unrealized gain on unconsolidated co-investment	(1,531)	(1,457)	0
(Loss) gain on early retirement of debt, net	(22,883)	3,717	0
Gain on remeasurement of co-investment	234,694	31,535	1,253
Net income	599,332	464,448	413,599
Assets:
Net reportable operating segments - real estate assets	10,927,786	10,348,660
Real estate under development	386,047	546,075
Co-investments	1,018,010	1,335,339
Real estate held for sale	57,938	0
Cash and cash equivalents, including restricted cash	84,041	81,094
Marketable securities	147,768	144,193
Notes receivable	195,104	134,365
Operating lease right-of-use assets	72,143	74,744
Prepaid expenses and other assets	47,340	40,935
Total assets	12,936,177	12,705,405
Rental and Other Property
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	1,486,150	1,450,628	1,390,870
Management and Other Fees from Affiliates
Revenues from External Customers and Long-Lived Assets [Line Items]
Management and other fees from affiliates	9,598	9,527	9,183
Operating Segments | Southern California
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net operating income	393,776	425,882	412,517
Assets:
Net reportable operating segments - real estate assets	3,993,275	4,139,104
Operating Segments | Southern California | Rental and Other Property
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	570,673	597,330	579,533
Operating Segments | Northern California
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net operating income	435,403	412,706	384,548
Assets:
Net reportable operating segments - real estate assets	5,520,019	4,408,404
Operating Segments | Northern California | Rental and Other Property
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	610,867	557,139	520,117
Operating Segments | Seattle Metro
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net operating income	166,847	172,601	163,927
Assets:
Net reportable operating segments - real estate assets	1,403,678	1,456,187
Operating Segments | Seattle Metro | Rental and Other Property
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	243,900	243,060	234,138
Other Real Estate Assets
Revenues from External Customers and Long-Lived Assets [Line Items]
Total net operating income	49,724	42,912	45,537
Assets:
Net reportable operating segments - real estate assets	10,814	344,965
Other Real Estate Assets | Rental and Other Property
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	$ 60,710	$ 53,099	$ 57,082