Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Aug. 31, 2015 USD ($)
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	$ 326,905	$ 327,078	$ 319,562	$ 312,178	$ 308,646	$ 302,522	$ 294,101	$ 280,229	$ 1,285,723	$ 1,185,498	$ 961,591
Net operating income									896,796	821,990	649,045
Management and other fees from affiliates									8,278	8,909	9,347
Depreciation and amortization									(441,682)	(453,423)	(360,592)
General and administrative									(40,751)	(40,090)	(40,878)
Merger and integration expenses									0	(3,798)	(53,530)
Acquisition and investment related costs									(1,841)	(2,414)	(1,878)
Interest expense									(219,654)	(204,827)	(164,551)
Total return swap income									11,716	5,655	0
Interest and other income									27,305	19,143	11,811
Equity income in co-investments									48,698	21,861	39,893
Loss on early retirement of debt									(606)	(6,114)	(268)
Gain on sale of real estate and land									154,561	47,333	46,039
Deferred tax expense on gain on sale of real estate and land									(4,410)	0	0
Gain on remeasurement of co-investment									0	34,014	0
Net income									438,410	248,239	134,438
Net reportable operating segments - real estate assets	10,364,760				10,381,577				10,364,760	10,381,577
Real estate under development	190,505				242,326				190,505	242,326
Co-investments	1,161,275				1,036,047			$ 13,700	1,161,275	1,036,047		$ 20,400
Real estate held for sale, net	101,957				26,879				101,957	26,879
Cash and cash equivalents, including restricted cash	170,302				123,055				170,302	123,055
Marketable securities	139,189				137,485				139,189	137,485
Notes and other receivables	40,970				19,285				40,970	19,285
Prepaid expenses and other assets	48,450				41,730				48,450	41,730
Total assets	12,217,408				12,008,384				12,217,408	12,008,384
Reportable Geographical Components [Member] | Southern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues									561,094	507,536	418,495
Net operating income									382,312	340,797	274,806
Net reportable operating segments - real estate assets	4,924,792				4,752,174				4,924,792	4,752,174
Reportable Geographical Components [Member] | Northern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues									453,140	407,590	319,082
Net operating income									325,394	291,168	223,559
Net reportable operating segments - real estate assets	3,791,549				3,733,218				3,791,549	3,733,218
Reportable Geographical Components [Member] | Seattle Metro [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues									217,259	201,417	168,337
Net operating income									148,279	136,579	112,494
Net reportable operating segments - real estate assets	1,570,340				1,613,175				1,570,340	1,613,175
Segment Reconciling Items [Member] | Other Real Estate Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues									54,230	68,955	55,677
Net operating income									40,811	53,446	$ 38,186
Net reportable operating segments - real estate assets	$ 78,079				$ 283,010				$ 78,079	$ 283,010