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Unsecured Senior Notes (Narrative) (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
May 05, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Debt Instrument [Line Items] |  |  |  |  |
Proceeds from unsecured senior notes |  | $ 1,248,125 |  | $ 1,548,106 | $ 996,410
Boston Properties Limited Partnership |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Proceeds from unsecured senior notes |  | $ 1,248,125 |  | $ 1,548,106 | $ 996,410
Debt Instrument, Covenant Description |  | The indenture relating to the unsecured senior notes contains certain financial restrictions and requirements, including (1) a leverage ratio not to exceed 60%, (2) a secured debt leverage ratio not to exceed 50%, (3) an interest coverage ratio of greater than 1.50, and (4) an unencumbered asset value of not less than 150% of unsecured debt. |  |  |
Debt Instrument, Covenant Compliance |  | At December 31, 2020, Boston Properties Limited Partnership was in compliance with each of these financial restrictions and requirements. |  |  |
Senior Notes | Boston Properties Limited Partnership |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Debt |  | $ 9,700,000 |  |  |
3.343 % unsecured senior notes [Member] | Senior Notes | Boston Properties Limited Partnership |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Debt | $ 1,250,000 | $ 1,250,000 |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 3.25% | 3.25% |  |  |
Senior Notes Pricing | 99.85% |  |  |  |
Debt Instrument, Interest Rate, Effective Percentage | 3.343% | 3.343% | [1] |  |
Proceeds from unsecured senior notes | $ 1,240,000 |  |  |  |
[1] | Yield on issuance date including the effects of discounts on the notes, settlements of interest rate contracts and the amortization of financing costs.

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