Segment Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)	Dec. 31, 2016 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]
Property revenues	$ 341,974	$ 327,078	$ 1,011,908	$ 958,818
Net operating income	237,837	227,717	709,993	668,888
Management and other fees from affiliates	2,395	2,093	6,927	6,145
Depreciation and amortization	(117,451)	(110,467)	(350,893)	(329,847)
General and administrative	(9,788)	(9,647)	(30,726)	(28,527)
Acquisition and investment related costs	(324)	(284)	(1,154)	(1,379)
Interest expense	(55,938)	(56,693)	(167,333)	(164,727)
Total return swap income	2,538	3,143	7,653	9,080
Interest and other income	5,790	4,943	17,916	19,560
Equity income from co-investments	19,727	9,568	40,934	38,932
Loss on early retirement of debt	0	(211)	0	(211)
Gain on sale of real estate and land	249	0	26,423	20,258
Deferred tax expense on gain on sale of real estate and land	0	0	0	(4,279)
Gain on remeasurement of co-investment	0	0	88,641	0
Net income	85,035	70,162	348,381	233,893
Net reportable operating segment - real estate assets	10,653,264		10,653,264		$ 10,364,760
Real estate under development	313,825		313,825		190,505
Co-investments	1,124,577		1,124,577		1,161,275
Real estate held for sale, net	0		0		101,957
Cash and cash equivalents, including restricted cash	63,273		63,273		170,302
Marketable securities	184,574		184,574		139,189
Notes and other receivables (includes related party receivables of $65.6 million and $11.3 million as of September 30, 2017 and December 31, 2016, respectively)	121,557		121,557		40,970
Prepaid expenses and other assets	51,453		51,453		48,450
Total assets	12,512,523		12,512,523		12,217,408
Operating Segments [Member] | Southern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	150,413	142,112	445,296	417,114
Net operating income	102,699	96,486	305,894	284,345
Net reportable operating segment - real estate assets	4,822,941		4,822,941		4,924,792
Operating Segments [Member] | Northern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	127,673	115,318	377,531	338,761
Net operating income	91,018	83,042	271,224	243,876
Net reportable operating segment - real estate assets	4,241,460		4,241,460		3,791,549
Operating Segments [Member] | Seattle Metro [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	58,285	55,543	171,564	161,192
Net operating income	39,674	37,688	116,733	109,352
Net reportable operating segment - real estate assets	1,532,784		1,532,784		1,570,340
Other real estate assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	5,603	14,105	17,517	41,751
Net operating income	4,446	$ 10,501	16,142	$ 31,315
Net reportable operating segment - real estate assets	$ 56,079		$ 56,079		$ 78,079