Segment Information - Performance of the Reportable Segments Based on Property Level Operating Income (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Segment Reporting Information [Line Items]
Operating revenue	$ 192,959,000		$ 151,024,000		$ 390,574,000		$ 298,150,000
Net operating income	62,470,000		51,452,000		121,928,000		98,378,000
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Interest expense	(38,470,000)		(28,133,000)		(77,677,000)		(55,872,000)
Depreciation and amortization expense					(116,547,000)		(90,956,000)
Gain on property dispositions	1,896,000		0		1,896,000		0
Equity in earnings of unconsolidated joint ventures	1,546,000		1,566,000		5,705,000		3,323,000
General and administrative expense	(14,973,000)		(16,455,000)		(33,334,000)		(36,248,000)
Income taxes	(693,000)		(660,000)		(1,224,000)		(1,151,000)
Income from continuing operations	29,866,000		29,577,000		56,198,000		54,410,000
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenue	0		0		0		0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenue	192,955,000		178,571,000		395,615,000		356,521,000
Net operating income	119,967,000		102,780,000		242,741,000		209,290,000
Operating Segments [Member] | Carolinas [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	8,486,000		7,309,000		16,803,000		14,587,000
Net operating income	5,693,000		4,939,000		11,435,000		9,853,000
Operating Segments [Member] | Chicago Milwaukee [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	8,152,000		3,470,000		16,723,000		6,163,000
Net operating income	4,973,000		1,812,000		10,136,000		3,986,000
Operating Segments [Member] | Houston [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	12,128,000		9,018,000		23,995,000		17,353,000
Net operating income	7,232,000		5,058,000		14,284,000		10,309,000
Operating Segments [Member] | Lehigh Central PA [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	28,195,000		24,681,000		57,819,000		49,358,000
Net operating income	19,773,000		16,550,000		39,013,000		33,218,000
Operating Segments [Member] | Minnesota [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	13,541,000		15,345,000		27,292,000		30,728,000
Net operating income	6,770,000		7,562,000		13,390,000		15,274,000
Operating Segments [Member] | Orlando [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	8,061,000		7,876,000		16,056,000		15,573,000
Net operating income	5,354,000		5,125,000		10,846,000		10,376,000
Operating Segments [Member] | Philadelphia [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	8,691,000		7,061,000		18,099,000		15,394,000
Net operating income	6,790,000		5,071,000		13,511,000		10,950,000
Operating Segments [Member] | Richmond Hampton Roads [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	10,115,000		9,794,000		20,184,000		19,940,000
Net operating income	6,054,000		5,853,000		11,973,000		12,079,000
Operating Segments [Member] | South Florida [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	11,707,000		8,676,000		24,016,000		17,234,000
Net operating income	6,891,000		4,858,000		14,418,000		9,433,000
Operating Segments [Member] | Southeastern PA [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	36,309,000		40,389,000		74,746,000		81,443,000
Net operating income	20,060,000		22,255,000		39,660,000		44,868,000
Operating Segments [Member] | Tampa [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	13,230,000		13,116,000		26,404,000		26,082,000
Net operating income	8,488,000		8,353,000		16,929,000		16,607,000
Operating Segments [Member] | United Kingdom [Member] | European Union [Member]
Segment Reporting Information [Line Items]
Operating revenue	4,218,000		1,120,000		8,320,000		2,220,000
Net operating income	2,722,000		(321,000)		6,248,000		(455,000)
Operating Segments [Member] | Other Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Operating revenue	30,122,000		30,716,000		65,158,000		60,446,000
Net operating income	19,167,000		15,665,000		40,898,000		32,792,000
Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Operating revenue	28,000		(27,516,000)		(4,735,000)		(58,597,000)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Operating revenue	(24,000)		(31,000)		(306,000)		226,000
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Interest expense	(38,470,000)	[1]	(32,138,000)	[1]	(78,234,000)	[1]	(64,220,000)	[1]
Depreciation and amortization expense	(44,561,000)	[2]	(29,061,000)	[2]	(89,098,000)	[2]	(58,368,000)	[2]
Gain on property dispositions	1,896,000		0		1,896,000		0
Equity in earnings of unconsolidated joint ventures	1,546,000		1,566,000		5,705,000		3,323,000
General and administrative expense	(8,232,000)	[2]	(8,945,000)	[2]	(20,633,000)	[2]	(22,821,000)	[2]
Discontinued operations excluding gain on property dispositions	(101,000)		(6,008,000)		(1,759,000)		(14,125,000)
Income taxes	(663,000)	[2]	(645,000)	[2]	(1,146,000)	[2]	(1,136,000)	[2]
Other	$ (1,516,000)		$ 2,028,000		$ (3,274,000)		$ 2,467,000

[1] Includes interest on discontinued operations.

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