Discontinued Operations (Details) (USD $)	3 Months Ended		9 Months Ended					9 Months Ended						12 Months Ended
	Sep. 30, 2014 sqft	Sep. 30, 2013	Sep. 30, 2014 sqft	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 San Diego Properties, San Diego [Member] building sqft		Sep. 30, 2014 10850 Via Frontera San Diego CA [Member]	Sep. 30, 2014 4040 Civic Center [Member] sqft building	Sep. 30, 2014 9785&9791 Towne Centre Drive, San Diego CA [Member] sqft building	Sep. 30, 2014 111 Pacifica [Member] [Member] sqft building	Sep. 30, 2014 2014 Dispositions [Member] sqft building	Sep. 30, 2014 999 Town &Country[Member] [Member] sqft building	Dec. 31, 2013 Restricted cash [Member]	Sep. 30, 2014 Properties Held for Sale [Member] building sqft
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of land (Note 13)	$ 0	$ 0	$ 3,490,000	$ 0
Dispositions Sales Price								33,100,000
Number of buildings						12	[1]		1	2	1	15	1		2	[2]
Proceeds from Sale of Real Estate Held-for-investment			368,381,000	14,409,000										32,200,000
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Disposal Group, Including Discontinued Operation, Land and improvements	18,077,000		18,077,000
Disposal Group, Including Discontinued Operation, Buildings and Improvements	31,530,000		31,530,000
Disposal Group, Including Discontinued Operation, Total real estate held-for-sale	49,607,000		49,607,000
Disposal Group, Including Discontinued Operation, Accumulated depreciation and amortization	5,046,000		5,046,000
Disposal Group, Including Discontinued Operation, Total real estate held for sale, net	44,561,000		44,561,000
Disposal Group, Including Discontinued Operation, Current receivables, net	56,000		56,000
Disposal Group, Including Discontinued Operation, Deferred rent receivables, net	1,241,000		1,241,000
Disposal Group, Including Discontinued Operation, Deferred leasing costs and acquisition-related intangible assets, net	3,754,000		3,754,000
Disposal Group, Including Discontinued Operation, Prepaid expenses and other assets, net	203,000		203,000
Disposal Group, Including Discontinued Operation, Real estate and other assets held for sale, net	49,815,000		49,815,000		213,100,000
Disposal Group, Including Discontinued Operation, Accounts payable, accrued expenses and other liabilities	944,000		944,000
Disposal Group, Including Discontinued Operation, Deferred revenue and acquisition-related intangible liabilities, net	1,733,000		1,733,000
Disposal Group, Including Discontinued Operation, Rents received in advance and tenant security deposits	422,000		422,000
Disposal Group, Including Discontinued Operations, Liabilities and deferred revenue of real estate assets held for sale	3,099,000		3,099,000		14,447,000
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Rental income	1,982,000	8,189,000	6,361,000	23,692,000
Tenant reimbursements	70,000	918,000	247,000	2,420,000
Other property income	6,000	5,151,000	26,000	5,159,000
Total revenues	2,058,000	14,258,000	6,634,000	31,271,000
Property expenses	705,000	2,673,000	1,952,000	5,753,000
Real estate taxes	196,000	891,000	628,000	2,626,000
Depreciation and amortization	609,000	4,846,000	1,963,000	11,693,000
Total expenses	1,510,000	8,410,000	4,543,000	20,072,000
Income from discontinued operations	548,000	5,848,000	2,091,000	11,199,000
Gains on dispositions of discontinued operations	5,587,000	0	110,391,000	423,000
Total income from discontinued operations	$ 6,135,000	$ 5,848,000	$ 112,482,000	$ 11,622,000
Net Rentable Area	79,000		79,000			1,049,035	[1]		130,237	126,000	67,496	1,242,531	98,551		228,788	[2]

[1] The San Diego Properties included the following: 10020 Pacific Mesa Boulevard, 6055 Lusk Avenue, 5010 and 5005 Wateridge Vista Drive, 15435 and 15445 Innovation Drive, and 15051, 15073, 15231, 15253, 15333 and 15378 Avenue of Science. These properties were held for sale as of December 31, 2013.

[2] Includes two properties, one located in Orange, California and the other in the San Rafael submarket of San Francisco, California.