Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) segment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 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	$ 308,646	$ 302,522	$ 294,101	$ 280,229	$ 276,778	$ 268,512	$ 256,952	$ 159,349	$ 1,185,498	$ 961,591	$ 603,327
Net operating income									821,990	649,045	405,991
Depreciation and amortization									(453,423)	(360,592)	(192,420)
Interest expense									(204,827)	(164,551)	(116,524)
Total return swap income									5,655	0	0
Management and other fees from affiliates									8,909	9,347	7,263
General and administrative									(40,090)	(40,878)	(26,684)
Merger and integration expenses									(3,798)	(53,530)	(4,284)
Acquisition and investment related costs									(2,414)	(1,878)	(1,161)
Interest and other income									19,143	11,811	11,633
Loss on early retirement of debt, net									(6,114)	(268)	(300)
Gains on sale of real estate and land									47,333	46,039	1,503
Equity income from co-investments									21,861	39,893	55,865
Gains on remeasurement of co-investment									34,014	0	0
Income before discontinued operations									248,239	134,438	140,882
Net reportable operating segment - real estate assets	10,381,577				9,679,875				10,381,577	9,679,875
Real estate under development	242,326				429,096				242,326	429,096
Co-investments	1,036,047			$ 13,700	1,042,423				1,036,047	1,042,423		$ 20,400
Real estate held for sale, net	26,879				56,300				26,879	56,300
Cash and cash equivalents, including restricted cash	123,055				95,749				123,055	95,749
Marketable securities and other investments	137,485				117,240				137,485	117,240
Notes and other receivables	19,285				24,923				19,285	24,923
Other non-segment assets	38,437				81,126				38,437	81,126
Total assets	12,005,091				11,526,732				12,005,091	11,526,732
Southern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues									529,440	423,570	263,582
Net operating income									355,007	279,434	176,075
Net reportable operating segment - real estate assets	4,912,264				4,277,754				4,912,264	4,277,754
Northern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues									416,347	326,996	210,831
Net operating income									297,472	228,971	146,053
Net reportable operating segment - real estate assets	3,749,072				3,418,571				3,749,072	3,418,571
Seattle Metro [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues									201,418	168,337	107,796
Net operating income									136,580	112,494	71,650
Net reportable operating segment - real estate assets	1,613,175				1,647,058				1,613,175	1,647,058
Other Real Estate Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total property revenues									38,293	42,688	21,118
Net operating income									32,931	28,146	$ 12,213
Net reportable operating segment - real estate assets	$ 107,066				$ 336,492				$ 107,066	$ 336,492