Acquisitions (Details) (USD $)	3 Months Ended
	Mar. 31, 2013 building sqft
Acquired operating properties from unrelated third parties
Rentable square feet	320,398
Purchase price	$ 170,000,000	[1]
Office Properties Acquisitions [Member]
Acquired operating properties from unrelated third parties
Number of buildings	2
320 & 321 Westlake Terry, Seattle WA [Member]
Acquired operating properties from unrelated third parties
Date of acquisition	Jan. 16, 2013	[2],[3]
Number of buildings	2	[2],[3]
Rentable square feet	320,398	[2],[3]
Occupancy as of March 31, 2013	100.00%	[2],[3]
Purchase price	170,000,000	[1],[2],[3]
Assets
Land and improvements	25,140,000
Buildings and improvements	142,021,000	[4]
Deferred leasing costs and acquisition-related intangible assets	16,019,000	[5]
Total assets acquired	183,180,000
Liabilities
Deferred revenue and acquisition-related intangible liabilities	1,570,000	[6]
Secured debt	95,496,000	[7]
Accounts payable, accrued expenses, and other liabilities	422,000
Total liabilities assumed	97,488,000
Net assets and liabilities acquired	$ 85,692,000	[8]

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

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

[3] 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).

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

[5] Represents in-place leases (approximately $13.0 million with a weighted average amortization period of 3.9 years), above-market leases (approximately $0.3 million with a weighted average amortization period of 4.6 years), and leasing commissions (approximately $2.7 million with a weighted average amortization period of 3.0 years).

[6] Represents below-market leases (approximately $1.6 million with a weighted average amortization period of 9.2 years).

[7] 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).

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