Segment Information (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of consolidated net operating income
Consolidated net operating income													$ 347,994	$ 332,615	$ 340,760
Less:
Interest expense													(131,405)	(132,640)	(135,740)
Deferred financing costs													(4,991)	(3,770)	(5,864)
Depreciation and amortization													(217,680)	(210,592)	(203,572)
Administrative expenses													(24,602)	(23,306)	(20,821)
Recognized Hedge Activity													0	0	(916)
Plus:
Interest income													1,813	3,222	2,499
Historic tax credit transaction income													12,026	0	0
Equity in income of real estate ventures													3,775	5,305	4,069
Net gain on sales of interests in real estate ventures													2,791	0	(3)
Net gain on sale of undepreciated real estate													45	0	0
Loss on real estate venture formation													(222)	0	0
Gain (loss) on early extinguishment of debt													(2,776)	(2,110)	23,176
Income (loss) from continuing operations													(13,232)	(31,276)	3,588
Income from discontinued operations													8,517	13,670	4,501
Net income (loss)	$ (4,602)	$ 6,611	$ (6,234)	[1]	$ (490)	[2]	$ (4,991)	$ (6,616)	$ (5,600)	[1]	$ (399)	[2]	$ (4,715)	$ (17,606)	$ 8,089

[1] The consolidated statement of operations for the second quarter of 2011 also contained an out of period depreciation and amortization expense adjustment of $4.7 million relating to intangible assets representing tenant relationships and in-place leases that should have been written off in prior periods. This resulted in the overstatement of depreciation and amortization expense by $4.7 million million in the current year. During the year ended December 31, 2010, depreciation and amortization expense was overstated by $1.7 million and was understated by $1.4 million, $1.8 million, $1.7 million and $1.5 million during the years ended December 31, 2009, 2008, 2007, and 2006, respectively. As management believes that this error was not material to prior years' consolidated financial statements and that the impact of recording the error in the current year is not material to the Company's consolidated financial statements, the Company recorded the related adjustment during the current year.

[2] During the first quarter of 2011, the Company recorded additional income of $0.5 million related to electricity charges in prior years that were under-billed to a certain tenant. This resulted in the overstatement of total revenue by $0.5 million during the current year and in the understatement of total revenue by $0.3 million and $0.2 million for the years ended December 31, 2009 and 2008, respectively. As management believes that this error was not material to prior years' consolidated financial statements and that the impact of recording the error in the current year is not material to the Company's consolidated financial statements, the Company recorded the related adjustment in the current year.