Segment Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 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	$ 1,400,053	$ 1,363,899	$ 1,294,001
Net operating income	1,005,536	978,939	926,906
Corporate-level property management expenses	(31,062)	(30,156)	(30,110)
Depreciation and amortization	(479,884)	(468,881)	(441,682)
General and administrative	(53,451)	(41,385)	(40,751)
Expensed acquisition and investment related costs	(194)	(1,569)	(1,841)
Interest expense	(220,492)	(222,894)	(219,654)
Total return swap income	8,707	10,098	11,716
Interest and other income	23,010	24,604	27,305
Equity income from co-investments	89,132	86,445	48,698
Loss on early retirement of debt	0	(1,796)	(606)
Gain on sale of real estate and land	61,861	26,423	154,561
Deferred tax expense on gain on sale of real estate and land	0	0	(4,410)
Gain on remeasurement of co-investment	1,253	88,641	0
Net income	413,599	458,043	438,410
Net reportable operating segments - real estate assets	10,156,553	10,592,776
Real estate under development	454,629	355,735
Co-investments	1,300,140	1,155,984
Cash and cash equivalents, including restricted cash	151,395	61,126
Marketable securities	209,545	190,004
Notes and other receivables (includes related party receivables of $11.1 million and $41.2 million as of December 31, 2018 and December 31, 2017, respectively)	71,895	100,926
Prepaid expenses and other assets	39,439	39,155
Total assets	12,383,596	12,495,706
Rental and other property [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	1,390,870	1,354,325	1,285,723
Management and other fees from affiliates [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	9,183	9,574	8,278
Operating Segments [Member] | Southern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	421,613	408,070	381,212
Net reportable operating segments - real estate assets	4,350,377	4,504,930
Operating Segments [Member] | Southern California [Member] | Rental and other property [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	592,281	574,552	540,000
Operating Segments [Member] | Northern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	386,401	371,795	333,757
Net reportable operating segments - real estate assets	4,270,238	4,220,551
Operating Segments [Member] | Northern California [Member] | Rental and other property [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	522,561	505,313	453,140
Operating Segments [Member] | Seattle Metro [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	165,397	162,253	154,147
Net reportable operating segments - real estate assets	1,472,916	1,522,452
Operating Segments [Member] | Seattle Metro [Member] | Rental and other property [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	236,525	229,871	217,259
Other real estate assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	32,125	36,821	57,790
Net reportable operating segments - real estate assets	63,022	344,843
Other real estate assets [Member] | Rental and other property [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues	$ 39,503	$ 44,589	$ 75,324