Significant Accounting Policies - Concentrations of Credit Risk/Accounting Standards Updates (Details) $ in Billions	3 Months Ended
Mar. 31, 2018 USD ($) Tenant
Annualized rent \| Customer concentration
Concentration of Credit Risk
Number of tenants (tenants) \| Tenant	1
Maximum percentage of annualized rent for any one tenant not individually disclosed (percent) (more than)	5.00%
Annualized rent \| 1515 Broadway \| Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	5.80%
Annualized rent \| 11 Madison Avenue \| Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	7.30%
Annualized rent \| 1185 Avenue of the Americas \| Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	7.30%
Annualized rent \| 420 Lexington Avenue \| Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	6.30%
Annualized rent \| 1 Madison Ave \| Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	5.70%
Tenant 1 \| Annualized rent \| Customer concentration
Concentration of Credit Risk
Percentage of concentration (percent)	8.20%
1515 Broadway \| Accounting Standards Update 2017-05
Concentration of Credit Risk
Gain on disposal \| $	$ 0.6

Represents the maximum percentage of concentration risk that is not individually disclosed.

No definition available.

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- Definition

Represents the number of tenants to whom the facility is leased.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
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-Section 50
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- Definition

Amount of the cumulative effect on retained earnings net of related income tax effect.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

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