Segment Information (Details) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Jan. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting [Abstract]
Number of reportable operating segments defined by geographical regions (in segments) | segment					3
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues			$ 366,932	$ 350,917	$ 1,084,790	$ 1,046,895
Net operating income			262,033	250,835	781,533	753,199
Corporate-level property management expenses			(8,255)	(7,761)	(24,620)	(23,313)
Depreciation and amortization			(120,809)	(120,852)	(360,842)	(359,287)
General and administrative			(11,345)	(10,601)	(38,731)	(36,539)
Expensed acquisition and investment related costs			(13)	(31)	(69)	(156)
Gain on sale of real estate and land			0	0	0	22,244
Interest expense			(54,896)	(55,196)	(162,651)	(166,335)
Total return swap income			2,154	2,184	6,174	6,682
Interest and other income			8,685	8,437	29,293	21,241
Equity income from co-investments			21,700	16,788	54,935	64,611
Deferred tax expense on unrealized gain on unconsolidated co-investment			(1,457)	0	(1,457)	0
Gain on early retirement of debt, net	$ 5,500	$ 1,400	5,475	0	7,143	0
Gain on remeasurement of co-investment			0	0	31,535	0
Net income			105,700	86,110	329,266	289,159
Net reportable operating segment - real estate assets	10,379,518		10,379,518		10,379,518		$ 10,156,553
Real estate under development	562,338		562,338		562,338		454,629
Co-investments	1,413,861		1,413,861		1,413,861		1,300,140
Cash and cash equivalents, including restricted cash	91,726		91,726	174,626	91,726	174,626	151,395	$ 61,126
Marketable securities	216,894		216,894		216,894		209,545
Notes and other receivables	216,541		216,541		216,541		71,895
Operating lease right-of-use assets	75,478		75,478		75,478		0
Prepaid expenses and other assets	41,536		41,536		41,536		39,439
Total assets	12,997,892		12,997,892		12,997,892		12,383,596
Rental and Other Property Revenues [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues			364,504	348,610	1,077,767	1,040,083
Management and Other Fees From Affiliates Income [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues			2,428	2,307	7,023	6,812
Operating Segments [Member] | Southern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income			106,951	104,732	323,073	314,977
Net reportable operating segment - real estate assets	4,245,335		4,245,335		4,245,335		4,350,377
Operating Segments [Member] | Southern California [Member] | Rental and Other Property Revenues [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues			152,312	148,575	455,302	442,382
Operating Segments [Member] | Northern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income			105,381	97,244	310,407	288,222
Net reportable operating segment - real estate assets	4,623,559		4,623,559		4,623,559		4,270,238
Operating Segments [Member] | Northern California [Member] | Rental and Other Property Revenues [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues			144,124	131,538	420,544	389,750
Operating Segments [Member] | Seattle Metro [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income			43,701	40,999	129,013	123,432
Net reportable operating segment - real estate assets	1,444,045		1,444,045		1,444,045		1,472,916
Operating Segments [Member] | Seattle Metro [Member] | Rental and Other Property Revenues [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues			61,657	59,231	182,738	176,740
Other real estate assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income			6,000	7,860	19,040	26,568
Net reportable operating segment - real estate assets	$ 66,579		66,579		66,579		$ 63,022
Other real estate assets [Member] | Rental and Other Property Revenues [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues			$ 6,411	$ 9,266	$ 19,183	$ 31,211