Subsequent Events (Details Textual) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				12 Months Ended				1 Months Ended		2 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Conexant Systems Lease Default [Member] Lease Concentration Risk [Member] Commercial Square Footage [Member]	Dec. 31, 2012 Conexant Systems Lease Default [Member] Lease Concentration Risk [Member] Minimum Base Rent [Member]	Jan. 31, 2013 Subsequent Event [Member]	Jan. 18, 2013 Subsequent Event [Member] sqft	Mar. 05, 2013 Subsequent Event [Member] Monument IV at Worldgate [Member]	Feb. 04, 2013 Subsequent Event [Member] Monument IV at Worldgate [Member] sqft
Subsequent Event [Line Items]
Operating lease, area under sublease by Conexant										115,000
Operating lease, percentage of premise under sublease by Conexant										57.00%
Concentration percentage							3.50%	5.50%
Retirement of note payable related to purchase of 111 Sutter Street									$ 12,000
Lease Term												3 years
Area of leased space												83,000
Lease Renewal Option												2 years
Common Stock, Dividends, Per Share, Declared	$ 0.09506	$ 0.09506	$ 0.09506	$ 0.09506	$ 0.38517	$ 0.09506					$ 0.10