Segment Reporting Reportable Segments (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014 segment		Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 169,441,000		$ 62,278,000		$ 464,915,000		$ 184,267,000
Interest expense	(17,674,000)				(46,640,000)
Depreciation, Depletion and Amortization, Nonproduction	(37,880,000)				(96,632,000)
Income tax expense	(3,004,000)				(4,153,000)
Income (Loss) from Equity Method Investments	0		14,816,000		0		14,816,000
Net Income (Loss) Attributable to Parent	8,322,000				22,525,000
Assets	3,302,016,000				3,302,016,000			2,476,061,000
Equity Method Investments	0		88,304,000		0		88,304,000		76,879,000
Number of reportable segments					2
Real Estate, Segment [Member]
Segment Reporting Information [Line Items]
Revenues	127,942,000		56,374,000		346,807,000		165,852,000
Operating Expenses, Excluding Noncash Items	(74,215,000)		(22,173,000)		(202,504,000)		(63,918,000)
Interest expense	(17,674,000)		(14,906,000)		(46,640,000)		(43,817,000)
Depreciation, Depletion and Amortization, Nonproduction	(37,797,000)		(12,763,000)		(96,404,000)		(38,030,000)
Income tax expense	(371,000)				(1,024,000)
Income (Loss) from Equity Method Investments			6,918,000				14,816,000
Assets	3,038,363,000		1,023,333,000		3,038,363,000		1,023,333,000
Equity Method Investments			88,304,000				88,304,000
Payments to Acquire Productive Assets	422,175,000		23,118,000		459,910,000		56,129,000
Observatory, Segment [Member] [Member]
Segment Reporting Information [Line Items]
Revenues	35,684,000				83,374,000
Operating Expenses, Excluding Noncash Items	(26,982,000)				(72,762,000)
Interest expense	0				0
Depreciation, Depletion and Amortization, Nonproduction	(79,000)				(217,000)
Income tax expense	(2,970,000)				(3,035,000)
Assets	255,081,000				255,081,000
Payments to Acquire Productive Assets	99,000				99,000
Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	5,815,000		5,869,000		33,759,000		18,269,000
Operating Expenses, Excluding Noncash Items	(7,365,000)		(7,623,000)		(36,052,000)		(24,651,000)
Interest expense	0		0		0		0
Depreciation, Depletion and Amortization, Nonproduction	(4,000)		0		(11,000)		0
Income tax expense	(75,000)				(94,000)
Income (Loss) from Equity Method Investments			0				0
Assets	8,572,000		10,585,000		8,572,000		10,585,000
Equity Method Investments			0				0
Payments to Acquire Productive Assets	0		0		0		0
Total, Segment [Member]
Segment Reporting Information [Line Items]
Revenues	169,441,000		62,243,000		463,940,000		184,121,000
Operating Expenses, Excluding Noncash Items	(108,562,000)		(29,796,000)		(311,318,000)		(88,569,000)
Interest expense	(17,674,000)		(14,906,000)		(46,640,000)		(43,817,000)
Depreciation, Depletion and Amortization, Nonproduction	(37,880,000)		(12,763,000)		(96,632,000)		(38,030,000)
Income tax expense	(3,416,000)				(4,153,000)
Income (Loss) from Equity Method Investments			6,918,000				14,816,000
Assets	3,302,016,000		1,033,918,000		3,302,016,000		1,033,918,000
Equity Method Investments			88,304,000				88,304,000
Payments to Acquire Productive Assets	422,274,000		23,118,000		460,009,000		56,129,000
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(21,474,000)		(1,942,000)		(54,903,000)		(6,786,000)
Intersegment Eliminations [Member] | Real Estate, Segment [Member]
Segment Reporting Information [Line Items]
Revenues	19,986,000	[1]	19,000	[1]	51,552,000	[1]	56,000
Intersegment Eliminations [Member] | Observatory, Segment [Member] [Member]
Segment Reporting Information [Line Items]
Revenues	0				0
Intersegment Eliminations [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,488,000		1,923,000		3,351,000		6,730,000
Intersegment Eliminations [Member] | Total, Segment [Member]
Segment Reporting Information [Line Items]
Revenues	21,474,000		1,942,000		54,903,000		6,786,000
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	190,915,000		64,185,000		518,843,000		190,907,000
Operating Segments [Member] | Real Estate, Segment [Member]
Segment Reporting Information [Line Items]
Revenues	147,928,000		56,393,000		398,359,000		165,908,000
Net Income (Loss) Attributable to Parent	17,871,000		13,469,000		51,787,000		34,959,000
Operating Segments [Member] | Observatory, Segment [Member] [Member]
Segment Reporting Information [Line Items]
Revenues	35,684,000				83,374,000
Net Income (Loss) Attributable to Parent	5,653,000				7,360,000
Operating Segments [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Revenues	7,303,000		7,792,000		37,110,000		24,999,000
Net Income (Loss) Attributable to Parent	(141,000)		169,000		953,000		348,000
Operating Segments [Member] | Total, Segment [Member]
Segment Reporting Information [Line Items]
Revenues	190,915,000		64,185,000		518,843,000		190,907,000
Net Income (Loss) Attributable to Parent	$ 23,383,000		$ 13,638,000		$ 60,100,000		$ 35,307,000

[1] The observatory pays a market-based rent payment comprised of fixed and percentage rent to the Empire State Building.