Property Table 1 Property Details (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2012 Monument IV at Worldgate [Member] Office Properties [Member] sqft	Aug. 27, 2004 Monument IV at Worldgate [Member] Office Properties [Member]	Dec. 04, 2012 111 Sutter Street [Member] sqft	Dec. 31, 2012 111 Sutter Street [Member] Office Properties [Member] sqft	Mar. 29, 2005 111 Sutter Street [Member] Office Properties [Member]	Dec. 31, 2012 105 Kendall Park Lane [Member] Industrial Properties [Member] sqft	Jun. 30, 2005 105 Kendall Park Lane [Member] Industrial Properties [Member]	Dec. 31, 2012 Dignity Health Office Portfolio 1 Office Properties [Member] sqft	Dec. 21, 2005 Dignity Health Office Portfolio 1 Office Properties [Member]	Dec. 31, 2012 Stirling Slidell Shopping Centre [Member] Retail Properties [Member] sqft	Dec. 14, 2006 Stirling Slidell Shopping Centre [Member] Retail Properties [Member]	Dec. 31, 2012 4001 North Norfleet Road [Member] Industrial Properties [Member] sqft	Feb. 27, 2007 4001 North Norfleet Road [Member] Industrial Properties [Member]	Dec. 31, 2012 Station Nine Apartments [Member] Apartment Properties [Member] sqft	Apr. 16, 2007 Station Nine Apartments [Member] Apartment Properties [Member]	Dec. 31, 2012 4 Research Park Drive [Member] Office Properties [Member] sqft	Jun. 13, 2007 4 Research Park Drive [Member] Office Properties [Member]	Dec. 31, 2012 36 Research Park Drive [Member] Office Properties [Member] sqft	Jun. 13, 2007 36 Research Park Drive [Member] Office Properties [Member]	Dec. 31, 2012 The District at Howell Mill [Member] Retail Properties [Member] sqft	Jun. 15, 2007 The District at Howell Mill [Member] Retail Properties [Member]	Dec. 31, 2012 Canyon Plaza [Member] Office Properties [Member] sqft	Jun. 26, 2007 Canyon Plaza [Member] Office Properties [Member]	Dec. 31, 2012 Railway Street Corporate Centre [Member] Office Properties [Member] sqft	Aug. 30, 2007 Railway Street Corporate Centre [Member] Office Properties [Member]	Dec. 31, 2012 Cabana Beach San Marcos [Member] Apartment Properties [Member] sqft	Nov. 21, 2007 Cabana Beach San Marcos [Member] Apartment Properties [Member]	Dec. 31, 2012 Cabana Beach Gainesville [Member] Apartment Properties [Member] sqft	Nov. 21, 2007 Cabana Beach Gainesville [Member] Apartment Properties [Member]	Dec. 31, 2012 Campus Lodge Athens [Member] Apartment Properties [Member] sqft	Nov. 21, 2007 Campus Lodge Athens [Member] Apartment Properties [Member]	Dec. 31, 2012 Campus Lodge Columbia [Member] Apartment Properties [Member] sqft	Nov. 21, 2007 Campus Lodge Columbia [Member] Apartment Properties [Member]	Dec. 31, 2012 The Edge at Lafayette [Member] Apartment Properties [Member] sqft	Jan. 15, 2008 The Edge at Lafayette [Member] Apartment Properties [Member]	Dec. 31, 2012 Campus Lodge Tampa [Member] Apartment Properties [Member] sqft	Feb. 29, 2008 Campus Lodge Tampa [Member] Apartment Properties [Member]
Business Acquisition [Line Items]
Area of Real Estate Property (in square feet)	228,000		286,000	286,000		409,000		755,000		139,000		702,000		312,000		60,000		81,000		306,000		199,000		137,000		278,000		545,000		229,000		256,000		207,000		431,000
Real Estate Property Ownership Percentage	100.00%			100.00%		100.00%		100.00%		100.00%		100.00%		100.00%		100.00%		100.00%		87.85%		100.00%		100.00%		78.00%		78.00%		78.00%		78.00%		78.00%		78.00%
Acquisitions and Disposals, Date of Transaction for Acquisition or Disposal	Aug. 27, 2004			Mar. 29, 2005		Jun. 30, 2005		Dec. 21, 2005		Dec. 14, 2006		Feb. 27, 2007		Apr. 16, 2007		Jun. 13, 2007		Jun. 13, 2007		Jun. 15, 2007		Jun. 26, 2007		Aug. 30, 2007		Nov. 21, 2007		Nov. 21, 2007		Nov. 21, 2007		Nov. 21, 2007		Jan. 15, 2008		Feb. 29, 2008
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds		$ 59,608	$ 62,845		$ 100,779		$ 18,781		$ 136,761		$ 23,367		$ 37,579		$ 56,417		$ 11,330		$ 17,232		$ 78,661		$ 54,973		$ 42,614		$ 29,375		$ 74,277		$ 20,980		$ 24,852		$ 26,870		$ 46,787