Discontinued Operations (Details) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended	1 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 Eastpointe Corporate Center [Member]	Sep. 30, 2011 Corporate Court 5000 [Member]	Sep. 20, 2011 W Wacker Building 35 [Member]	Sep. 30, 2011 Secured Debt [Member] Mortgage Note, 35 West Wacker Building [Member]	Dec. 31, 2010 Secured Debt [Member] Mortgage Note, 35 West Wacker Building [Member]	Sep. 30, 2011 Land [Member]	Dec. 31, 2010 Land [Member]	Sep. 30, 2011 Building Improvements [Member]	Dec. 31, 2010 Building Improvements [Member]	Sep. 30, 2011 Construction in Progress [Member]	Dec. 31, 2010 Construction in Progress [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percent of Ownership Interest In Real Estate Property Disposal								96.50%
Real Estate Property Disposal, Sale Price								$ 401,000,000
Net sales proceeds from wholly-owned properties			68,041,000	0		31,700,000	36,300,000
Real estate assets held for sale, net:
Property, Plant, and Equipment, Net											55,573,000	55,573,000	167,024,000	164,343,000	2,673,000	2,560,000
Property, Plant, and Equipment, Accumulated Depreciation													41,754,000	37,442,000
Intangible lease assets	3,626,000		3,626,000		5,802,000
Intangible lease assets, accumulated amortization	22,725,000		22,725,000		20,549,000
Real estate assets held for sale, net	228,896,000		228,896,000		228,278,000
Other assets held for sale:
Tenant receivables	11,790,000		11,790,000		10,737,000
Deferred financing costs, net	49,000		49,000		66,000
Deferred financing costs, accumulated amortization	169,000		169,000		153,000
Deferred lease costs, net	24,067,000		24,067,000		27,480,000
Deferred lease costs, accumulated amortization	29,353,000		29,353,000		26,055,000
Restricted cash and escrows	11,447,000		11,447,000		11,661,000
Other assets held for sale	47,353,000		47,353,000		49,944,000
Notes payable and other liabilities held for sale:
Notes payable	120,000,000		120,000,000		120,000,000
Notes payable, interest rate									5.10%	5.10%
Notes payable, maturity date									Jan. 01, 2014	Jan. 01, 2014
Intangible lease liabilities, less accumulated amortization of $25,960 and $23,458 as of September 30, 2011 and December 31, 2010, respectively	4,451,000		4,451,000		6,954,000
Intangible lease liabilities, less accumulated amortization	25,960,000		25,960,000		23,458,000
Total notes payable and other liabilities held for sale	124,451,000		124,451,000		126,954,000
Noncontrolling interest held for sale	2,797,000		2,797,000		4,623,000
Revenues:
Rental Income	7,477,000	10,273,000	24,631,000	30,455,000
Tenant Reimbursement	3,565,000	2,708,000	14,303,000	14,046,000
Revenue	11,042,000	12,981,000	38,934,000	44,501,000
Expenses:
Property Operating Costs	3,403,000	2,395,000	15,712,000	14,637,000
Depreciation	1,516,000	1,694,000	4,912,000	5,541,000
Amortization of deferred leasing costs	1,676,000	1,716,000	5,093,000	5,193,000
General and administrative expense	45,000	171,000	80,000	195,000
Expenses	6,640,000	5,976,000	25,797,000	25,566,000
Other income (expense):
Interest expense	(1,568,000)	(1,583,000)	(4,653,000)	(4,697,000)
Interest and other income	16,000		1,000	2,000
Net income attributable to noncontrolling interest	(131,000)	(154,000)	(366,000)	(397,000)
Other income (expense)	(1,683,000)	(1,737,000)	(5,018,000)	(5,092,000)
Operating income, excluding impairment loss and gain on sale	2,719,000	5,268,000	8,119,000	13,843,000
Impairment loss	0	0	0	(9,587,000)
Gain on sale of real estate assets	26,756,000	0	26,756,000	0		12,200,000	14,600,000
Income from discontinued operations	$ 29,475,000	$ 5,268,000	$ 34,875,000	$ 4,256,000