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Properties Held for Sale and Property Dispositions (Details) $ in Millions	1 Months Ended
	Jan. 31, 2018 USD ($) ft²	Jun. 30, 2018 ft²
Properties Sold [Abstract]
Approximate Square Feet | ft²		31,150,063
600 Lexington Ave
Properties Sold [Abstract]
Approximate Square Feet | ft²	303,515
Sales Price	$ 305.0
Gain on Sale (Loss)	$ 23.8
115-117 Stevens Avenue
Properties Sold [Abstract]
Approximate Square Feet | ft²	178,000
Sales Price	$ 12.0
Gain on Sale (Loss)	$ (0.7)
635 Madison Avenue
Properties Sold [Abstract]
Approximate Square Feet | ft²	176,530
Sales Price	$ 153.0
Gain on Sale (Loss)	$ (14.1)

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Properties Sold [Abstract]

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Area of a real estate property.

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Amount after tax of gain (loss) not previously recognized resulting from the disposal of a discontinued operation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1361-107760

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=65878427&loc=SL51721525-107759

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5C
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-URI http://asc.fasb.org/extlink&oid=64827811&loc=SL51721675-107760

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
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-URI http://asc.fasb.org/extlink&oid=65878427&loc=d3e957-107759

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Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

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