Segment Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of reportable operating segments (in segments) | segment	3
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	$ 282,607	$ 255,848
Corporate-level property management expenses	(8,759)	(8,429)
Depreciation and amortization	(131,559)	(120,568)
General and administrative	(13,982)	(13,459)
Expensed acquisition and investment related costs	(87)	(32)
Interest expense	(55,147)	(53,643)
Total return swap income	1,984	2,045
Interest and other income (loss)	(5,221)	12,261
Equity income from co-investments	21,297	16,276
Gain on early retirement of debt, net	321	1,336
Gain on remeasurement of co-investment	234,694	31,535
Net income	328,765	125,505
Net reportable operating segment - real estate assets	11,428,118		$ 10,348,660
Real estate under development	435,865		546,075
Co-investments	997,137		1,335,339
Cash and cash equivalents, including restricted cash	282,347	124,126	81,094	$ 151,395
Marketable securities	148,139		144,193
Notes and other receivables	34,867		134,365
Operating lease right-of-use assets	74,428		74,744
Prepaid expenses and other assets	49,940		40,935
Total assets	13,450,841		12,705,405
Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	389,750	353,888
Management and Other Fees From Affiliates Income
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	2,617	2,335
Operating Segments | Southern California
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	111,097	107,996
Net reportable operating segment - real estate assets	4,198,656		4,233,110
Operating Segments | Southern California | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	155,642	151,463
Operating Segments | Northern California
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	120,981	101,214
Net reportable operating segment - real estate assets	5,748,062		4,622,268
Operating Segments | Northern California | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	164,079	136,745
Operating Segments | Seattle Metro
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	44,993	41,699
Net reportable operating segment - real estate assets	1,469,297		1,481,061
Operating Segments | Seattle Metro | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	63,844	60,413
Other real estate assets
Revenues from External Customers and Long-Lived Assets [Line Items]
Net operating income	5,536	4,939
Net reportable operating segment - real estate assets	12,103		$ 12,221
Other real estate assets | Rental and Other Property Revenues
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 6,185	$ 5,267