Acquisitions (Details) (USD $)	3 Months Ended
	Mar. 31, 2014 sqft
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement	Mar. 13, 2014
Rentable square feet	79,000
401 Terry Avenue North, Seattle, WA [Member]
Business Acquisition [Line Items]
Number of buildings	1
Rentable square feet	140,605
Occupancy as of March 31, 2014	100.00%
Purchase price	$ 106,100,000
Office Properties Acquisitions [Member]
Business Acquisition [Line Items]
Number of buildings	1
Assets
Land and improvements	22,500,000
Buildings and improvements	77,046,000	[1]
Deferred leasing costs and acquisition-related intangible assets	11,199,000	[2]
Total assets acquired	110,745,000
Liabilities
Deferred revenue and acquisition-related intangible liabilities	4,620,000	[3]
Total liabilities assumed	4,620,000
Net assets and liabilities acquired	$ 106,125,000

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

[2] Represents in-place leases of approximately $9.3 million (with a weighted average amortization period of seven years) and leasing commissions of approximately $1.9 million (with a weighted average amortization period of seven years).

[3] Represents below-market leases of approximately $4.6 million (with a weighted average amortization period of seven years).