Segment Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) segment	Mar. 31, 2016 USD ($)	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	$ 333,168	$ 312,178
Net operating income	233,655	217,688
Management and other fees from affiliates	2,236	2,024
Depreciation and amortization	(115,503)	(109,707)
General and administrative	(10,601)	(9,182)
Acquisition and investment related costs	(556)	(828)
Interest expense	(54,583)	(52,466)
Total return swap income	2,584	3,123
Interest and other income	6,764	5,208
Equity income from co-investments	10,899	15,068
Gain on sale of real estate and land	26,174	20,258
Deferred tax expense on gain on sale of real estate and land	0	(4,279)
Gain on remeasurement of co-investment	86,482	0
Net income	187,551	86,907
Net reportable operating segment - real estate assets	10,792,684		$ 10,364,760
Real estate under development	239,685		190,505
Co-investments	1,071,258		1,161,275
Real estate held for sale, net	0		101,957
Cash and cash equivalents, including restricted cash	100,252		170,302
Marketable securities	138,977		139,189
Notes and other receivables (includes related party receivables of $10.3 million and $11.3 million as of March 31, 2017 and December 31, 2016, respectively)	50,855		40,970
Prepaid expenses and other assets	53,716		48,450
Total assets	12,447,427		12,217,408
Reportable Geographical Components [Member] | Southern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	147,099	135,894
Net operating income	101,405	92,654
Net reportable operating segment - real estate assets	4,885,678		4,924,792
Reportable Geographical Components [Member] | Northern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	123,308	110,408
Net operating income	87,663	79,013
Net reportable operating segment - real estate assets	4,293,943		3,791,549
Reportable Geographical Components [Member] | Seattle Metro [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	56,192	52,073
Net operating income	38,933	35,689
Net reportable operating segment - real estate assets	1,555,853		1,570,340
Segment Reconciling Items [Member] | Other Real Estate Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	6,569	13,803
Net operating income	5,654	$ 10,332
Net reportable operating segment - real estate assets	$ 57,210		$ 78,079