Acquisitions (Details) (USD $)	3 Months Ended
	Mar. 31, 2012 RSF NumberofBuildings
Acquired operating properties from unrelated third parties
Number of Buildings	7
Rentable square feet	374,139
Purchase Price	$ 162,500,000
Bohannon Drive Menlo Park, CA [Member]
Assets
Land	38,810,000
Buildings and improvements	124,617,000	[1]
Deferred leasing costs and acquisition-related intangible assets	9,470,000	[2]
Total assets acquired	172,897,000
Liabilities
Deferred revenue and acquisition-related intangible liabilities	10,380,000	[3]
Accounts payable, accrued expenses, and other liabilities	137,000
Total liabilities assumed	10,517,000
Net assets and liabilities acquired	162,380,000	[4]
Office Properties [Member]
Acquired operating properties from unrelated third parties
Number of Buildings	7
Rentable square feet	374,139
Office Properties [Member] | Bohannon Drive Menlo Park, CA [Member]
Acquired operating properties from unrelated third parties
Number of Buildings	7
Date of Acquisition	February 29, 2012
Rentable square feet	374,139
Occupancy as of March 31, 2012	80.10%
Purchase Price	$ 162,500,000	[5]

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

[2] Represents in-place leases (approximately $5.8 million with a weighted average amortization period of 5.8 years), above-market leases (approximately $0.1 million with a weighted average amortization period of 2.6 years), and leasing commissions (approximately $3.5 million with a weighted average amortization period of 4.3 years).

[3] Represents below-market leases (approximately $10.4 million with a weighted average amortization period of 8.2 years).

[4] Reflects the purchase price net of other lease-related obligations.

[5] Excludes acquisition-related costs.