Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Segment Information [Abstract]
Number of reportable operating segments defined by geographical regions	3
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	$ 125,474	$ 111,208
Net operating income	85,310	72,784
Depreciation	(40,734)	(36,658)
Interest expense before amortization	(24,658)	(21,811)
Amortization expense	(2,871)	(2,851)
Management and other fees from affiliates	2,444	1,224
General and administrative	(5,400)	(5,274)
Cost of management and other fees	(1,640)	(925)
Interest and other income	2,413	6,987
Equity income (loss) from co-investments	2,340	(1,373)
Income before discontinued operations	17,204	12,103
Real estate assets	3,389,013		3,393,038
Real estate under development	45,632		44,280
Co-investments	401,531		383,412
Cash and cash equivalents, including restricted cash	37,347		35,463
Marketable securities	80,000		74,275
Funds held by 1031 exchange facilitator	10,984		0
Notes and other receivables	48,053		66,369
Other non-segment assets	38,818		40,127
Total assets	4,051,378		4,036,964
Southern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	58,560	53,863
Net operating income	39,830	35,384
Real estate assets	1,450,624		1,478,018
Northern California [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	41,622	35,317
Net operating income	28,942	23,339
Real estate assets	1,255,836		1,241,320
Seattle Metro [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	22,309	19,756
Net operating income	14,831	12,557
Real estate assets	592,320		579,612
Other Real Estate Assets [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Property revenues	2,983	2,272
Net operating income	1,707	1,504
Real estate assets	$ 90,233		$ 94,088