Segment Information - Performance of the Reportable Segments Based on Property Level Operating Income (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Segment Reporting Information [Line Items]
Operating revenue	$ 198,356,000		$ 155,348,000		$ 588,946,000		$ 453,498,000
Net operating income	66,330,000		52,413,000		188,145,000		150,791,000
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Interest expense	(37,958,000)		(33,542,000)		(115,635,000)		(89,414,000)
Depreciation and amortization expense					(176,207,000)		(137,302,000)
(Loss) gain on property dispositions	(20,000)		0		1,879,000		0
Equity in earnings of unconsolidated joint ventures	1,592,000		650,000		7,297,000		3,973,000
General and administrative expense	(14,748,000)		(17,217,000)		(48,077,000)		(53,466,000)
Income taxes	(859,000)		(629,000)		(2,083,000)		(1,780,000)
Income from continuing operations	35,315,000		23,404,000		91,388,000		77,839,000
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenue	0		0		0		0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenue	198,350,000		183,237,000		593,962,000		539,757,000
Net operating income	124,521,000		109,293,000		367,264,000		318,582,000
Operating Segments [Member] | Carolinas [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	9,479,000		7,626,000		26,282,000		22,213,000
Net operating income	6,570,000		5,182,000		18,006,000		15,035,000
Operating Segments [Member] | Chicago Milwaukee [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	8,004,000		3,067,000		24,727,000		9,230,000
Net operating income	5,382,000		2,163,000		15,518,000		6,149,000
Operating Segments [Member] | Houston [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	12,833,000		9,481,000		36,828,000		26,833,000
Net operating income	7,510,000		5,426,000		21,794,000		15,735,000
Operating Segments [Member] | Lehigh Central PA [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	30,034,000		24,981,000		87,853,000		74,339,000
Net operating income	21,634,000		17,204,000		60,647,000		50,422,000
Operating Segments [Member] | Minnesota [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	13,925,000		15,591,000		41,217,000		46,319,000
Net operating income	6,575,000		7,289,000		19,964,000		22,563,000
Operating Segments [Member] | Orlando [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	8,463,000		7,583,000		24,519,000		23,156,000
Net operating income	5,411,000		5,128,000		16,257,000		15,504,000
Operating Segments [Member] | Philadelphia [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	8,303,000		7,633,000		26,402,000		23,027,000
Net operating income	6,736,000		5,919,000		20,247,000		16,869,000
Operating Segments [Member] | Richmond Hampton Roads [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	10,358,000		9,959,000		30,542,000		29,899,000
Net operating income	6,144,000		5,899,000		18,118,000		17,978,000
Operating Segments [Member] | South Florida [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	12,012,000		8,798,000		36,028,000		26,032,000
Net operating income	6,647,000		4,735,000		21,066,000		14,168,000
Operating Segments [Member] | Southeastern PA [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	36,087,000		41,251,000		110,833,000		122,694,000
Net operating income	20,516,000		23,754,000		60,175,000		68,622,000
Operating Segments [Member] | Tampa [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	13,597,000		12,767,000		40,001,000		38,849,000
Net operating income	8,213,000		7,916,000		25,142,000		24,522,000
Operating Segments [Member] | United Kingdom [Member] | European Union [Member]
Segment Reporting Information [Line Items]
Operating revenue	4,111,000		1,400,000		12,430,000		3,620,000
Net operating income	2,468,000		123,000		8,716,000		(331,000)
Operating Segments [Member] | Other Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	31,144,000		33,100,000		96,300,000		93,546,000
Net operating income	20,715,000		18,555,000		61,614,000		51,346,000
Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Operating revenue	(9,000)		(28,007,000)		(4,728,000)		(86,604,000)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenue	15,000		118,000		(288,000)		345,000
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Interest expense	(37,958,000)	[1]	(37,412,000)	[1]	(116,192,000)	[1]	(101,632,000)	[1]
Depreciation and amortization expense	(44,538,000)	[1],[2]	(29,963,000)	[1],[2]	(133,636,000)	[1],[2]	(88,330,000)	[1],[2]
(Loss) gain on property dispositions	(20,000)		0		1,879,000		0
Equity in earnings of unconsolidated joint ventures	1,592,000		650,000		7,297,000		3,973,000
General and administrative expense	(8,556,000)	[1],[2]	(12,394,000)	[1],[2]	(29,189,000)	[1],[2]	(35,215,000)	[1],[2]
Discontinued operations excluding gain on property dispositions	(98,000)		(6,515,000)		(1,985,000)		(20,641,000)
Income taxes	(821,000)	[2]	(636,000)	[2]	(1,966,000)	[2]	(1,772,000)	[2]
Other	$ 1,193,000		$ 381,000		$ (2,084,000)		$ 2,874,000

[1] Includes activity on discontinued operations.

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