Real Estate Investments (Details Textuals) (USD $)	Sep. 30, 2011	Aug. 12, 2011 sqft	Jan. 20, 2011	Mar. 28, 2011 Overlook I And II [Member] sqft	Jan. 20, 2011 Parcel of land in PA [Member]	Jan. 20, 2011 Parcel of land in PA [Member] Partnership Interest [Member]	Jun. 30, 2011 Three Logan Square [Member] sqft	Aug. 05, 2010 Three Logan Square [Member] Storey	Aug. 05, 2010 Three Logan Square [Member] Partnership Interest [Member] Units
Real Estate Investments (Textuals) [Abstract]
Net rentable space of property acquired		192,707		126,496			1,000,000
Recognized tenant and other receivables from acquisition								$ 1,100,000
Prepaid real estate taxes from acquisition								1,500,000
Advance under credit facility		600,000,000
Acquisition related costs		300,000			500,000			400,000
Number of storey of office tower acquired								53
Business Acquisition, Equity Interest Issued or Issuable, Description						50% limited interest in the partnership
Business Acquisition, Equity Interest Issued or Issuable			50.00%
Business Acquisition, consideration received					4,900,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Units									7,111,112
Lease percentage of acquired property	57.20%			100.00%			67.20%
Acquisitions through cash								51,200,000
Assumed security deposits obligations	700,000							900,000
Closing market price of Parent Company's common shares on acquisition date								11.54
Annual dividend rate per share								$ 0.60
Net amount of cash paid after assumed liabilities								50,300,000
Acquired real estate, cost of property		18,800,000		12,600,000	9,300,000			129,000,000
Business acquisition, purchase price allocated to building		21,400,000
Business acquisition, purchase price allocated to intangible assets		12,000,000
Business acquisition, purchase price allocated to market lease liabilities		14,400,000
Business acquisition, purchase price allocated to other assets		200,000
Business acquisition, purchase price allocated to assumed liabilities		$ 400,000