Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Nominal or face amount used to calculate payments on the derivative asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Fixed interest rate related to the interest rate derivative.

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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.

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- Definition

Nominal or face amount used to calculate payments on the derivative liability.

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Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Derivative and Hedging Instruments Derivative Instrument and Hedging Activities Notional Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value	$ (6,133)	$ (47,144)	$ (10,302)
Boston Properties Limited Partnership \| Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Notional Amount		550,000
767 Fifth Partners LLC [Member] \| Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Liability, Notional Amount		350,000
Derivative Asset, Notional Amount		100,000
Derivative, Notional Amount		450,000
Fair Value		(8,264)
Other Liabilities [Member] \| 767 Fifth Partners LLC [Member] \| Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value		$ (8,773)
Other Liabilities [Member] \| Minimum [Member] \| 767 Fifth Partners LLC [Member] \| Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Fixed Interest Rate		2.418%
Other Liabilities [Member] \| Maximum [Member] \| 767 Fifth Partners LLC [Member] \| Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Fixed Interest Rate		2.95%
Prepaid Expenses and Other Assets [Member] \| 767 Fifth Partners LLC [Member] \| Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair Value		$ 509
Prepaid Expenses and Other Assets [Member] \| Minimum [Member] \| 767 Fifth Partners LLC [Member] \| Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Fixed Interest Rate		2.336%
Prepaid Expenses and Other Assets [Member] \| Maximum [Member] \| 767 Fifth Partners LLC [Member] \| Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Fixed Interest Rate		2.388%