Segment Information - Performance of the Reportable Segments Based on Property Level Operating Income (Details) (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
Segment Reporting Information [Line Items]
Operating revenue	$ 169,801	$ 166,247	$ 165,027	$ 166,519	$ 164,530	$ 166,316	$ 161,789	$ 164,366	$ 667,594		$ 657,001		$ 644,696
Segment-level operating revenue									725,214		750,274		759,673
Interest expense									(122,018)		(134,384)		(133,997)
Equity in earnings of unconsolidated joint ventures									3,496		2,296		2,161
Impairment charges - investment in unconsolidated joint ventures and other									0		(378)		(82,552)
Impairment charges - goodwill									0		0		(15,700)
Income (Loss) from continuing operations before income taxes									140,891		131,738		31,020
Northeast Southeastern PA [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									174,063		181,412		185,158
Northeast Southeastern PA [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									174,063		181,412		185,158
Net Operating Income									101,982		108,593		112,148
Northeast Lehigh/Central PA [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									99,311		103,802		101,473
Northeast Lehigh/Central PA [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									99,311		103,802		101,473
Net Operating Income									64,786		66,632		65,827
Northeast Other [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									70,582		74,660		82,221
Northeast Other [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									70,582		74,660		82,221
Net Operating Income									35,017		37,234		43,953
Central Region [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									126,268		125,501		129,340
Central Region [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									126,268		125,501		129,340
Net Operating Income									68,114		70,386		73,249
South Region [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									222,004		232,071		235,021
South Region [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									222,004		232,071		235,021
Net Operating Income									132,703		136,135		140,361
Metro [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									28,578		28,617		22,057
Metro [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									28,578		28,617		22,057
Net Operating Income									19,370		20,713		15,525
United Kingdom [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									4,408		4,211		4,403
United Kingdom [Member] | Statement, Geographical, Foreign [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									4,408		4,211		4,403
Net Operating Income									(178)		243		1,293
Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment-level operating revenue									725,214		750,274		759,673
Segment-level net operating income									421,794		439,936		452,356
Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Operating revenue									(57,828)		(93,097)		(115,021)
Corporate Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenue									208		(176)		44
Significant Reconciling Items [Member]
Segment Reporting Information [Line Items]
Interest expense									(131,046)	[1]	(149,704)	[1]	(151,764)	[1]
Depreciation and amortization									(106,487)	[2]	(109,265)	[2]	(109,474)	[2]
Gain on property dispositions									5,025		4,616		1,687
Equity in earnings of unconsolidated joint ventures									3,496		2,296		2,161
General and administrative									(36,140)	[2]	(32,805)	[2]	(31,056)	[2]
Discontinued Operations excluding gain on property dispositions									(10,257)		(16,516)		(30,607)
Impairment charges - investment in unconsolidated joint ventures and other									0		(378)		(82,552)
Impairment charges - goodwill									0		0		(15,700)
Other reconciling items to Total Income before income taxes									$ (5,494)		$ (6,442)		$ (4,031)

[1] Includes interest on discontinued operations.

[2] Excludes costs which are included in determining segment-level net operating income.