Segment Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 USD ($)	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	$ 336,766	$ 319,562	$ 669,934	$ 631,740
Net operating income	238,501	223,483	472,156	441,171
Management and other fees from affiliates	2,296	2,028	4,532	4,052
Depreciation and amortization	(117,939)	(109,673)	(233,442)	(219,380)
General and administrative	(10,337)	(9,698)	(20,938)	(18,880)
Acquisition and investment related costs	(274)	(267)	(830)	(1,095)
Interest expense	(56,812)	(55,568)	(111,395)	(108,034)
Total return swap income	2,531	2,814	5,115	5,937
Interest and other income	5,362	9,409	12,126	14,617
Equity income from co-investments	10,308	14,296	21,207	29,364
Gain on sale of real estate and land	0	0	26,174	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	2,159	0	88,641	0
Net income	75,795	76,824	263,346	163,731
Net reportable operating segment - real estate assets	10,721,057		10,721,057		$ 10,364,760
Real estate under development	263,284		263,284		190,505
Co-investments	1,081,084		1,081,084		1,161,275
Real estate held for sale, net	3,015		3,015		101,957
Cash and cash equivalents, including restricted cash	199,876		199,876		170,302
Marketable securities	151,995		151,995		139,189
Notes and other receivables (includes related party receivables of $11.0 million and $11.3 million as of June 30, 2017 and December 31, 2016, respectively)	54,660		54,660		40,970
Prepaid expenses and other assets	49,980		49,980		48,450
Total assets	12,524,951		12,524,951		12,217,408
Operating Segments [Member] | Southern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	147,784	139,108	294,883	275,002
Net operating income	101,790	95,205	203,195	187,859
Net reportable operating segment - real estate assets	4,854,134		4,854,134		4,924,792
Operating Segments [Member] | Northern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	126,550	113,035	249,858	223,443
Net operating income	92,543	81,821	180,206	160,834
Net reportable operating segment - real estate assets	4,266,100		4,266,100		3,791,549
Operating Segments [Member] | Seattle Metro [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	57,087	53,576	113,279	105,649
Net operating income	38,126	35,975	77,059	71,664
Net reportable operating segment - real estate assets	1,544,364		1,544,364		1,570,340
Other real estate assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	5,345	13,843	11,914	27,646
Net operating income	6,042	$ 10,482	11,696	$ 20,814
Net reportable operating segment - real estate assets	$ 56,459		$ 56,459		$ 78,079