Acquisitions, Dispositions and Other Information Property Acquisition (Details) (USD $)			3 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 2100 Ross Avenue [Member] sqft
Business Acquisition [Line Items]
Area of Real Estate Property			844,000
Real Estate Acquisition Cash Paid			$ 59,200,000
Business Acquisition, Purchase Price Allocation, Liabilities Assumed			4,200,000
Business Combination, Acquisition Related Costs			369,000
Land and improvements			5,987,000
Building			36,705,000
Tenant improvements			9,034,000
Tangible Assets			51,726,000
Above-market leases	9,369,000	8,845,000	3,267,000
In-Place Leases	5,099,000	2,833,000	8,888,000
Total Intangible Assets			12,155,000
Below-Market Leases			(436,000)
Total net assets acquired			$ 63,445,000