Discontinued Operations Discontinued Operations (Details) (USD $)	3 Months Ended			9 Months Ended				3 Months Ended				9 Months Ended						3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended			9 Months Ended					3 Months Ended
	Sep. 30, 2012 NumberofBuildings		Sep. 30, 2011	Sep. 30, 2012 NumberofBuildings		Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Total Property Dispositions [Member]		Sep. 30, 2011 Total Property Dispositions [Member]		Sep. 30, 2012 Total Property Dispositions [Member]		Sep. 30, 2011 Total Property Dispositions [Member]		Sep. 30, 2012 15004 Innovation Drive and 10243 Genetic Center Drive, San Diego, CA [Member] sqft NumberofBuildings		Sep. 30, 2012 Office Properties [Member] NumberofBuildings	Sep. 30, 2011 Office Properties [Member]	Sep. 30, 2012 Office Properties [Member] NumberofBuildings	Sep. 30, 2011 Office Properties [Member]	Sep. 30, 2012 All Other Segments [Member]	Sep. 30, 2011 All Other Segments [Member]	Sep. 30, 2012 All Other Segments [Member]	Sep. 30, 2011 All Other Segments [Member]	Sep. 30, 2012 Assets Held-for-sale [Member] NumberofBuildings sqft	Sep. 30, 2012 Industrial Property [Member] sqft NumberofBuildings		Sep. 30, 2012 Carmino Ruiz CA [Member] sqft NumberofBuildings	Sep. 30, 2012 E. La Palma Avenue, Anaheim, California [Member] NumberofBuildings sqft	Oct. 31, 2011 Mortgage Loan Total Property Dispositions [Member] property	Sep. 30, 2011 Office Building [Member] NumberofBuildings	Sep. 30, 2011 Industrial Property [Member] NumberofBuildings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Number of Buildings																																2	1
Property Type																Office											Industrial	[1]	Office	Office
Month of Disposition																January	[2]
Number of buildings	12			12												2	[2]	111		111						44	39	[1]	4	1
Rentable Square Feet																253,676										3,721,989	3,413,354	[1]	265,372	43,263
Sales Price																$ 146,100,000
Land																										57,553,000
Buildings and improvements	3,169,224,000			3,169,224,000			2,830,310,000																			206,488,000
Total real estate held for investment	4,399,353,000			4,399,353,000			3,798,690,000																			264,041,000
Accumulated depreciation	(725,728,000)			(725,728,000)			(742,503,000)																			(109,404,000)
Total real estate assets held for investment, net	3,673,625,000			3,673,625,000			3,056,187,000																			154,637,000
Current receivables, net																										176,000
Deferred rent receivables, net	110,128,000			110,128,000			101,142,000																			6,637,000
Deferred leasing costs and acquisition-related intangible assets, net	187,307,000	[3]		187,307,000	[3]		155,522,000																			3,053,000
Prepaid expenses and other assets, net	24,398,000			24,398,000			12,199,000																			1,516,000
Real estate assets and other assets held for sale, net	166,019,000			166,019,000			84,156,000																			166,019,000
Accounts Payable and Accrued Liabilities	127,472,000			127,472,000			81,713,000																			2,044,000
Deferred Revenue And Acquisition Related Intangible Liabilities	120,407,000			120,407,000			79,781,000																			371,000
Rents received in advance and tenant security deposits	31,728,000			31,728,000			26,917,000																			2,040,000
Liabilities and deferred revenue of real estate assets held for sale	4,455,000			4,455,000			13,286,000																			4,455,000
Rental income	95,405,000		79,673,000	268,228,000		223,853,000		5,945,000		10,046,000		18,476,000		29,608,000
Tenant reimbursements	8,665,000		6,387,000	23,947,000		17,382,000		995,000		1,352,000		3,216,000		4,289,000
Other property income	223,000		339,000	1,625,000		2,136,000		142,000		9,000		220,000		727,000
Total revenues								7,082,000		11,407,000		21,912,000		34,624,000
Property expenses	21,871,000		18,132,000	57,906,000		49,091,000		1,189,000		1,262,000		3,912,000		5,575,000
Real estate taxes	9,312,000		7,352,000	25,138,000		21,941,000		735,000		1,037,000		2,249,000		3,030,000
Provision for bad debts	0		144,000	2,000		265,000		(194,000)		(149,000)		(194,000)		(124,000)
Depreciation and amortization	44,109,000		33,275,000	116,832,000		88,969,000		2,165,000		2,976,000		6,818,000		8,841,000
Interest expense								0	[4]	1,155,000	[4]	0	[4]	3,484,000	[4]
Total expenses								3,895,000		6,281,000		12,785,000		20,806,000
Income from discontinued operations before net gain on dispositions of discontinued operations	3,187,000		5,126,000	9,127,000		13,818,000		3,187,000		5,126,000		9,127,000		13,818,000
Mortgage loan																															70,000,000
Net gain on dispositions of discontinued operations	0		12,555,000	72,809,000		12,555,000		0		12,555,000		72,809,000		12,555,000
Total income from discontinued operations	$ 3,187,000		$ 17,681,000	$ 81,936,000		$ 26,373,000		$ 3,187,000		$ 17,681,000		$ 81,936,000		$ 26,373,000				$ (470,000)	$ 14,413,000	$ 72,572,000	$ 18,746,000	$ 3,657,000	$ 3,268,000	$ 9,364,000	$ 7,627,000
Debt Instrument, Collateral, Number of Properties																															13

[1] Includes all industrial properties owned by the Company at September 30, 2012.

[2] Properties were classified as held-for-sale on the consolidated balance sheets as of December 31, 2011.

[3] Balances and accumulated amortization amounts at September 30, 2012 reflect the write-off of the following fully amortized amounts at January 1, 2012: deferred leasing costs (approximately $9.5 million), above-market leases (approximately $1.6 million), in-place leases (approximately $3.7 million), and below-market leases (approximately $1.0 million).

[4] Interest expense relates to a $70.0 million mortgage loan that was secured by thirteen of our industrial properties. The mortgage loan was repaid in October 2011 prior to maturity.