Acquisitions (Details) (USD $)			9 Months Ended
	Sep. 30, 2013 building	Dec. 31, 2012	Sep. 30, 2013 Office Properties Acquisitions [Member] sqft building		Sep. 30, 2013 320 & 321 Westlake Terry, Seattle WA [Member] building sqft		Sep. 30, 2013 12780 and 12790 El Camino Real, Sandiego, CA [Member] sqft building		Jun. 27, 2013 Redwood City Partners, LLC [Member]
Business Acquisition [Line Items]
Date of Acquisition					Jan. 16, 2013	[1],[2]	Sep. 19, 2013	[3]
Number of buildings	14		4		2	[1],[2]	2	[3]
Rentable square feet			539,338		320,398	[1],[2]	218,940	[3]
Occupancy as of September 30, 2013					100.00%	[1],[2]	100.00%	[3]
Purchase price			$ 296,400,000	[4]	$ 170,000,000	[1],[2],[4]	$ 126,400,000	[3],[4]
Assets
Undeveloped land and construction in progress									11,222,000
Land and improvements			53,790,000	[5]
Buildings and improvements			218,211,000	[5],[6]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Undeveloped Land And Construction-in-Progress			9,360,000	[5],[7]
Deferred leasing costs and acquisition-related intangible assets			30,789,000	[5],[8]
Total assets acquired			312,150,000	[5]					11,222,000
Liabilities
Deferred revenue and acquisition-related intangible liabilities			4,190,000	[5],[9]
Secured debt			95,496,000	[10],[5]					1,750,000	[11]
Accounts payable, accrued expenses, and other liabilities			422,000	[5]					1,952,000
Total liabilities assumed			100,108,000	[5]					3,702,000
Noncontrolling interest	55,486,000	46,303,000							4,885,000
Net assets and liabilities acquired			$ 212,042,000	[12],[5]					$ 2,635,000

[1] We acquired these properties through a new special purpose entity wholly owned by the Finance Partnership.

[2] In connection with this acquisition, we assumed secured debt with an outstanding principal balance of $83.9 million that was recorded at fair value on the acquisition date, resulting in a premium of approximately $11.6 million (see Note 5).

[3] As of September 30, 2013, these properties, together the “Heights of Del Mar” project, are temporarily being held in a separate VIE to facilitate potential Section 1031 Exchanges (see Note 1). The $126.4 million purchase price includes $9.4 million for 4.2 acres of undeveloped land the Company acquired in connection with this acquisition.

[4] Excludes acquisition-related costs and includes assumed tenant improvements.

[5] The purchase price of the two acquisitions completed during the nine months ended September 30, 2013 were individually less than 5% and in aggregate less than 10% of the Company’s total assets as of September 30, 2013.

[6] Represents buildings, building improvements and tenant improvements.

[7] In connection with one of the acquisitions, we acquired undeveloped land of approximately 4.2 acres that was added to the Company’s future development pipeline upon acquisition.

[8] Represents in-place leases (approximately $19.6 million with a weighted average amortization period of 4.7 years), above-market leases (approximately $3.2 million with a weighted average amortization period of 6.1 years), and leasing commissions (approximately $7.9 million with a weighted average amortization period of 5.9 years).

[9] Represents below-market leases (approximately $4.2 million with a weighted average amortization period of 7.7 years).

[10] Represents the mortgage loan, which includes an unamortized premium of approximately $11.6 million at the date of acquisition, assumed in connection with the properties acquired in January 2013 (see Note 5).

[11] This note was repaid as of September 30, 2013.

[12] Reflects the purchase price net of assumed secured debt and other lease-related obligations.