Segment Information - Performance of the Reportable Segments Based on Property Level Operating Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Segment Reporting Information [Line Items]
Operating revenue	$ (169,937)		$ (166,134)
Interest expense	(28,476)		(32,889)
Equity in earnings of unconsolidated joint ventures	916		534
Income tax expense	(178)		(550)
Income (Loss) from continuing operations before income taxes	35,691		30,714
Northeast Southeastern PA [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Operating revenue	(42,195)		(45,265)
Net Operating Income	25,170		25,524
Northeast Lehigh/Central PA [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Operating revenue	(24,077)		(28,200)
Net Operating Income	16,195		17,449
Northeast Other [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Operating revenue	(17,400)		(18,293)
Net Operating Income	9,105		9,194
Central Region [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Operating revenue	(32,144)		(31,692)
Net Operating Income	17,747		17,472
South Region [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Operating revenue	(54,012)		(56,364)
Net Operating Income	32,654		34,002
Metro [Member] | Segment, Geographical, Domestic [Member]
Segment Reporting Information [Line Items]
Operating revenue	(8,188)		(7,149)
Net Operating Income	5,629		5,957
United Kingdom [Member] | Statement, Geographical, Foreign [Member]
Segment Reporting Information [Line Items]
Operating revenue	(1,162)		(1,132)
Net Operating Income	(229)		(49)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenue	(179,178)		(188,095)
Net Operating Income	106,271		109,549
Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Operating revenue	(9,409)		(21,961)
Corporate Elimination [Member]
Segment Reporting Information [Line Items]
Operating revenue	(168)		0
Significant Reconciling Items [Member]
Segment Reporting Information [Line Items]
Interest expense	(30,904)	[1]	(36,169)	[1]
Depreciation and amortization	(25,652)	[2]	(28,406)	[2]
Gain on property dispositions	523		1,161
Equity in earnings of unconsolidated joint ventures	916		534
General and administrative	(11,550)	[2]	(10,449)	[2]
Discontinued Operations excluding gain on property dispositions	(2,847)		(3,759)
Income tax expense	(178)		(550)
Other reconciling items to Total Income before income taxes	$ (888)		$ (1,197)

[1] Includes interest on discontinued operations.

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